> Windows itself keeps changing my default media player and image viewer back to the Microsoft defaults

Same here, and it's maddening. That kind of bullshit, along with OneDrive ads in the freaking file browser, and now the subject of this article, have pushed me completely off of Windows.

Now that Steam Play exists and works with every Windows-only game I've thrown at it, I have absolutely nothing holding me to Windows on my gaming PC and workstations at home. I still have to deal with WSE 2016 and Windows 7 Pro at work, but that decision is not up to me and even if it were, we'd still have to stay with Windows for some of our software. The owner would absolutely love to make us a Mac house all the way but she understands why we can't make that move.

And the default PDF viewer... Apparently some Windows updates change the user-defined PDF viewer to Edge.

Yes, I've seen this on Windows 10 Pro since 1803. Hilariously, it fails to open PDF's on an SMB share, says the file can't be found while listing its path. And the Microsoft Store is still so shady that I don't trust installing anything from a non-recognized vendor, so I ended up going to Adobe's web site to get Acrobat Reader which can open PDFs whether local or on that same SMB share.

It's because "Feature Updates" are actually in-place OS upgrades. They're essentially reinstalling Windows and migrating applications and settings, but also choosing to not migrate some of them.

Is that true? Does that mean that applications with a more complex setup will break with every feature update?

I would be okay with that if the previous setting is Acrobat Reader.

Perhaps you would - but somebody else's form filling just stopped working. Hey, no big deal: MS knows better than the user "where do you want to go today."

That usually happens if that media player or image viewer edits registry to associate file types

The design is slightly evil in that any unauthorized change of the registry keys doesn't just fail but instead invalidates a hash and makes windows revert to the default.

There is no API difference between registry changes made by nonsanboxed user installed and built-in windows executables.

I don't know exactly how it's implemented, and feel free to tell us, but wongarsu is absolutely correct about the behavior. For a while, whenever I hit the button in firefox to change default browser, suddenly my default browser was edge. Not the old setting, not the attempted new setting. It was very clearly not designed with 'protection' in mind.

There's a hash of the registry key stored "securely" somewhere. Only the API the control panel default apps UI uses changes this registry key and updates the hash. When the application key is called to run and doesn't match the hash it's reset to the value from "C:\Windows\System32\OEMDefaultAssociations.xml"

It's terrible behavior.

What sorts of locks/permissions does this file have?

Maybe you could make a tool that lets you make changes, schedules a modification of this file on next restart, and after the restart it propagates the changes in the registry too.

Yes, "please reboot to apply your new mouse position^W^W^Wfile association changes", yay, but that'd work.

Although I'd definitely hate it.

Does direct editing via regedit work as expected or does it also reset?

It will trigger a reset because you haven't updated the hash...

Which is bizarre if you consider that the original purpose of the registry (which appeared in Windows 3.1, I believe) was only to store file associations.