New
#11
I did some more testing upon getting back home, can clarify some things further. Here's the gist, for affected people:
If you use a local account to log in to Windows, and for any reason you authenticate into some OS-tied application with your MSA (xbox app, windows store app, and such), your "Default apps" settings will no longer be able to be changed.
If you use a local account to log in to Windows, change to using your MSA to log in (even after doing the above), suddenly your "Default apps" settings will behave as they should.
If you revert from using MSA to log in and go back to your local account, they will once again be unable to be changed. But if you swap back to MSA login again, the "Default apps" settings will behave as they should for the duration that you continue to log in with your MSA.
I've bounced back and forth multiple times rebooting here and there testing various things. Tried changing my sync settings to see if maybe that was causing it, still have no idea of the underlying mechanics, but those are the events.
So I guess another "solution" is to swap your local login to an MSA one, make the changes you need, then un-link it once you're done. While tedious, it's a lot less drastic than having to do a major system restore or a reinstall. Can just bounce on, make your defaults changes, and bounce back out. Most people probably aren't changing those all the time anyway.
Given that this is dealing with settings being 'locked' in a sense, I'm kind of getting the feeling that this is a new bug introduced by the patch that solved the bug where Windows 10 was forcibly resetting users' defaults repeatedly. Just a guess though.
Anyway, go forth with this limited resolution. I do hope it works out for the other people who have experienced it in this thread, and maybe any other random folks that hit this via google can get something out of it. Fingers crossed it gets fixed for real in the next major update.