If you have Chrome as the default browser on your Windows 10 computer, you'd better check to make sure Microsoft didn't hijack it last week and set Edge as your new default. The same goes for any PDF viewer: A forced cumulative update also reset PDF viewing to Edge on many PCs.
Do you use IrfanView, Acdsee, Photoshop Express, or Elements? The default photo app may have been reset to -- you guessed it -- the Windows Photos app. Music? Video? Microsoft may have swooped down and changed you over to Microsoft Party apps, all in the course of last week's forced cumulative update KB 3135173 .
Post pjfarr on Windows TenForums says:
My PC updated Windows 10 yesterday afternoon ("Cumulative Update for Windows 10 Version 1511 for x64-based Systems KB3135173)". After rebooting, it completely screwed all my custom file associations (mostly for media files: photos, audio, and video). A few minutes after the reboot, the Action Center started firing popups at me, one after the other, every few seconds:
"An app default was reset. An app caused a problem with the default setting for .avi files so it was reset to Films & TV." with a different file extension for each popup (avi, bmp, mp4, and so on) . Even .pdf files were changed from Adobe Reader to Microsoft Edge. As well, all my custom context menu items for these same file types were also deleted. I spent a lot of time setting these associations up and now they were all obliterated. I'd backed them all up in a .reg file but running it didn't do anything. So with a heavy (and angry) sigh I started manually changing the associations back to the way I had them. However, each time I finished making a change within seconds the Action Center would fire the same message as before at me for the file type I'd just changed and it would be reset back to the MS default again.
Finally in exasperation, I just used System Restore to go back before the updates and that solved the problem. Now, the Action Center keeps nagging me to set a time to reinstall this same update. I know I can't block it indefinitely, and there are probably important security patches in it I should have. So the question is: How can I stop it from f'ing up my file associations again?
Poster travelgirl on the Technet forums has a similar problem:
EVERYTIME i tell irfanview to retake the default for jpg, png, etc, the OS annoyingly claws them back with repeated "an app caused a problem"... i did NOT have this problem before today's updates to the OS.
To add insult to injury, KB 3135173 was the first Windows 10 patch that received anything resembling a changelog. As you might expect, the changelog doesn't describe anything along these lines. In fact the whole incident looks like a bug, pure and simple.
Ramesh Srinivasan at The Winhelponline blog put together a lengthy registry fix that seems to circumvent the problem.
Others have found respite by uninstalling KB 3135173 and blocking it from running again using the wushowhide utility buried in KB 3073930.
How many times does this have to happen before Microsoft separates security and non-security patches, and give us tools to block or delay patches? As long as Microsoft's patching bugs are relatively minor, there's little incentive to give us the tools we need. The day we get a really bad, crippling patch, there'll be tar and feathers.
The time to fix the problem is now.
t/h Susan Bradley