In order to prevent malware from hijacking popular file extensions, anytime an application "improperly" tries to set itself as a default app, it will revert to the Windows 10 default instead.

If you are having issues with this, it's probably bring caused by a legacy app or script doing something in a way that is no longer allowed.

But what if I explicitly select a non-Microsoft app to open a PDF, or JPG? Why does Windows systematically and consistently override my choice every few days? It's very aggravating.

Oh. That’s a bit subtle. Sounds like a good explanation though. Would be great if W10 logged this somewhere or in some other way gave the user a hint as to what is happening.

When that happens, you should get a notification that says something like:

> An app default was reset

> An app caused a problem with the default setting for .png files, so it was rest to Photos.

It does get logged and is viewable with the Event Viewer. Useful for sysadmins, but not end users.

I might be wrong, of course, but the OS should respect the user preference.

The OS must not, under any condition, override the user preference - especially, as you say, in case of "malware hijacking popular file extension".

The reason Microsoft do this is to respect the user preferences[1]. When a program goes through the proper channels, Windows pops up the dialog which says "you have installed a new program which can handle {Foo} filetype, would you like to open it in the new program, or the one you were using?"

When a program skips this user-respecting dialog, and edits the registry directly to take control of a file extension without user consent, Windows detects it and resets, to give control back to the user instead of letting random software take over. It's part of Raymond Chen's "What if two programs did this?[2]" and "I bet someone got a nice payrise for hijacking user file extensions" comments on his OldNewThing blog.

[1] https://devblogs.microsoft.com/oldnewthing/20170517-00/?p=96...

[2] https://devblogs.microsoft.com/oldnewthing/20050607-00/?p=35...

[3] See also: https://devblogs.microsoft.com/oldnewthing/20190724-00/?p=10...

I really don't understand your reasoning.

Let me clarify the scenario:

1. the user modified the default application for PDF to use FoxIt.

2. Win10 reverts the assignment back to Edge after an update and/or reboot.

There is no other program involved. There is a user setting the preference and Win10 ignoring it, consistently for a period of several years, ever since I installed it.

I haven’t experienced that in a while (IIRC it was at least 1,5 years ago). E.g. W10 1903 has not done that to me.

Does anyone here know if it’s possible for »mere mortals« to send in bug reports to the Windows team…? If so, you might want to do that. Or does that require going through some kind of intermediary?

Look for feedback hub in your start menu.

Ok. But that’s not really like logging a support ticket, right?

I'm not sure I've ever heard of anyone having this problem aside from that large server update a year or two ago and their "desktop experience". Can anyone tell me more?

Well, last year [0][1] consumers weren't able to have changes to the defaults. Well, some apps would change, but others wouldn't.

However, you can get the impression it happens more regularly because when individual default apps, like Photos, get updated (or if there is a problem in the registry) they may reset the association for the files they expect to handle.

[0] https://wccftech.com/windows-10-bug-unable-apps-defaults/

[1] https://support.microsoft.com/en-us/help/4467682/windows-10-...

Somehow it seems to do some braindead syncing when you set up a new device. When setting up a new laptop suddenly my desktop task bar switched sides to match the change on the laptop, and files stopped showing extensions (even though that wasn't touched yet on the laptop, the default is not to show them and that somehow seemed to carry over to my desktop).

Literally today it opened a PDF file with Edge for me. And, of course, file association page does not have a searh box to help find .txt among hundreds of useless and unassigned extensions.

See: https://devblogs.microsoft.com/oldnewthing/20170517-00/?p=96... for an explanation.

"A customer reported that each time they restart their Windows 10 PC, the file association for PDF documents keeps getting reset to the default, which is Microsoft Edge. [..]"

This is not a case of Program X messing with registry. This is the user explicitly setting Program X to be the default application.

I guess there is no way (given the current registry design) to differentiate between the user modifying the registry and a program modifying the registry.

Again, coming back to the original message - the case scenario is not that some program is changing the preferences. It the user changing the setting, and Win10 silently discarding the user input (after a reboot or some automated update).

I see it on every large update (like 1909) or so.