Csdrhrt

I've had this problem frequently but randomly. I was finally able to track down one set of triggers for the issue, but not a direct fix... only hackish, partial workarounds.

Workaround:

For example, "Groove" or "Movies & TV" will try to grab the associations of music and video formats. The only solution I have found is to uninstall these seemingly uninstallable programs.

http://www.howtogeek.com/224798/how-to-uninstall-windows-10s-built-in-apps-and-how-to-reinstall-them/

The above article describes how to use (admin)Power Shell to temporarily uninstall some Microsoft installed apps.

For example:

Get-AppxPackage *zunemusic* | Remove-AppxPackage

or

Get-AppxPackage *zunevideo* | Remove-AppxPackage

After uninstalling these apps, Windows 10 has never tried to re-take these file associations. I was half expecting it to try regardless and break the associations completely, but was fortunate.

Unfortunately this will not fix all of these problems. PDFs will continue to revert to Microsoft Edge because it cannot be uninstalled by this method.

Trigger cause:

I was able to track down a trigger that causes this to one of my programs. Though I'm not certain that it is the only one that does it as it only causes some associations to change. So more likely it is certain actions that the program causes sets up the first trigger; and another program completes the trigger sequence.

According to procmon, it does some registry snooping with file associations. The second trigger is to open a program that is associated with a file type that often reverts. That second program also snoops at file associations according to procmon.

What I imagine happens is that the first program does something to corrupt the "protection" Windows 10 has for programs changing file associations. Opening the second program causes Windows to re-check its protection and when the hash/progid ends up being invalid, it gets reverted to Microsoft defaults.

For example, I can see an old version of PhotoShop and Firefox doing this. They both look at the key

HKCUSOFTWAREMicrosoftWindowsCurrentVersionExplorerFileExts.pdfUserChoice

Program 1 messes up the hash/progid somehow, Program 2 which is associated with the type makes Windows re-check it and revert it. I'm a little mystified as to why it's deemed corrupted to begin with because the file association is correct before and after Program 1 does its thing. The association wasn't hijacked, so it didn't need Microsoft's overreach to begin with.

Not all of my systems have the same programs installed, so I'm guessing there may be many esoteric old programs that cause the first trigger event. Aside from my original workaround above, I guess you could be mindful using the offending programs. (shrug)

An explanation and solution is given at ghacks.

You can either use Stop Resetting My Apps which was developed to stop this resetting

or modify the registry by hand.

So, here is what you need to do for that if you prefer the manual way:

1. Tap on the Windows-key, type regedit.exe and hit the Enter-key. This opens the Windows Registry Editor. If you can, open a second Registry window for easier handling of the following operations.


2. Navigate to the following key: HKEY_CURRENT_USERSOFTWAREClassesLocal SettingsSoftwareMicrosoftWindowsCurrentVersionAppModelRepositoryPackages


3. Locate the application you want to block from being the default, and open AppCapabilitiesFileAssociations there. This displays the list of file associations of that particular application.


4. Take note of the value in Data, it looks like a long random string: AppXsq3757nydv3f9bx6862hv0t4z7ennqqd


5. Please note that this string may be different for any of the file types or protocols listed there.


6. Switch to the second Registry Editor window, and go to HKEY_CURRENT_USERSOFTWAREClassesThatRandomString, e.g. HKEY_CURRENT_USERSOFTWAREClassesAppXsq3757nydv3f9bx6862hv0t4z7ennqqd


7. Right-click on it, and select New > String Value.


8. Name it NoOpenWith, and keep its value empty.

Repeat the process for any file association that you don't want that particular app to be ever associated with again.

Several apps like Edge, Groove or Photo took over control of your files when you upgraded to Windows10, you will then not be able to choose your own software of your liking to open your files. BUT this behaviour can be stopped if you add a setting to your registry to Exclude E.g. Edge as an "available" file handler for PDF files. Following will stop Edge for blocking the use of Acrobat to open PDF files and other software like FIREFOX to open HTM and HTML files (I use the word BLOCK because Edge acts like a VIRUS, it always resets the file association back to Edge, even my 20th attempt to associate Acrobat Pro or Reader was re-set after a few hours, sometimes seconds.. ).
Now to the Regedit setting. You need to look-up the associated PROGRAM-ID inside the registry AND then create a new key for the FILE TYPE you want to exclude from that program.
The following entry....

[HKEY_CURRENT_USERSOFTWAREClassesLocal SettingsSoftwareMicrosoftWindowsCurrentVersionAppModelRepositoryPackagesMicrosoft.MicrosoftEdge_25.10586.0.0_neutral__8wekyb3d8bbweMicrosoftEdgeCapabilitiesFileAssociations]

".htm"="AppX4hxtad77fbk3jkkeerkrm0ze94wjf3s9"

".html"="AppX4hxtad77fbk3jkkeerkrm0ze94wjf3s9"

".pdf"="AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723"

".svg"="AppXde74bfzw9j31bzhcvsrxsyjnhhbq66cs"

".xml"="AppXcc58vyzkbjbs4ky0mxrmxf8278rk9b3t"

...shows that for PDF

AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723

is that PROGRAM-ID.

Now you go to...
HKEY_CURRENT_USERSOFTWAREClassesAppXd4nrz8ff68srnhf9t5a8sbjyar1cr723
(note the same ID)
and create a new STRING key
NoOpenWith
(leave it empty)

EXAMPLE (as long as MS does not change the IDs) the following will stop Edge to hijack .HTM .HTML and .PDF files:

Windows Registry Editor Version 5.00



[HKEY_CURRENT_USERSOFTWAREClassesAppX4hxtad77fbk3jkkeerkrm0ze94wjf3s9]

"NoOpenWith"=""



[HKEY_CURRENT_USERSOFTWAREClassesAppXd4nrz8ff68srnhf9t5a8sbjyar1cr723]

"NoOpenWith"=""

(you can copy this to a text file, change extension to .reg and import it to your registry.)

If you remove those 2 keys NoOpenWith again, it will revert to original setting.

I've found a way prevent edge from becoming the pdf / html handler. It's possible by adding the Noopenwith value for Edge's ProgID (the AppX..... key, this may vary from system to system). More details on it here. How to Stop Edge From Hijacking Your PDF or HTML Associations? The same method works for any other app.

This problem is likely caused by KB3135173 update (from February 9, 2016). The workaround is to uninstall the update and block it from reinstalling by using "Show or hide updates" troubleshooter package.

Source: @Jukin.Kei post at An App Default Was Reset at Microsoft Answers.

Related: Windows 10 now blocking IrfanView at Reddit.

Other workarounds:

• How to Stop Edge From Hijacking Your PDF or HTML Associations?


• Fix for “An App Default was Reset” Windows 10 Resetting File Associations (Registry Fixes)


• How to Stop Photos App from Resetting Image File Associations?

Also see that thing (update / install program that can open some files can lead to that dialog, if not disabled)
http://www.tenforums.com/software-apps/14819-windows-asks-default-program-even-after-being-set-disable.html

Here's another cause of this, for me at least:

SageThumbs 2.0.0.23

All was working well when I installed the original version of Windows 10,

But now when I recently re-installed:

Microsoft Windows [Version 10.0.15063]

SageThumbs did not work as expected and this problem appeared, I un-installed it, rebooted, set default apps, rebooted and problem is gone now :)

I opened an issue here for that problem.

By the way, it also appears that:

Winamp 5.666

Does not work well anymore, as it does not appear as an option to be the default app for music.

UI automation of the Settings app seems like, unfortunately, the best option here.

I created a simple AutoHotkey (AHK) script to set my browser to Firefox on startup (you need to compile the AHK script first, then I just set it to run "late" after login). The browser is determined by the number of TABs to get to your browser of choice.

Tested on Windows 10, build 1809.

; Fix default browser



    Sleep 1250

    SendInput {RWin}

    Sleep 1000

    Send Default apps

    Sleep 3500

    Send {enter}

    Sleep 3500

    Send {tab}

    Sleep 250

    Send {tab}

    Sleep 250

    Send {tab}

    Sleep 250

    Send {tab}

    Sleep 250

    Send {tab}

    Sleep 250

    Send {enter}

    Sleep 2000

    Send {tab}

    Sleep 250

    Send {enter}

    Sleep 7500

    Send !{F4}

    Sleep 100

Another potential solution is to change what your default associations are, so that when windows DOES revert to default associations, it reverts to what you want it to be.

See https://technet.microsoft.com/en-us/library/hh825038.aspx

DOES THIS APPLY TO WIN 10? Heading of the linked page does not say that.

For windows 10
After the installation of KB3135173 and how to