Since that update (KB3135173), I keep getting told that PDF is reset to Edge, JPG is reset to Photos, and MP3 is reset to Groove Music, but nothing actually happens to my file preferences. Windows 10 just keeps announcing that it made the changes, on a daily, or slightly less often, basis. It doesn't seem to be associated with any task in the Task Scheduler, either. I checked the logs at the time of the message. It just keeps telling me that "an app caused a problem" so it's resetting my preferences in those three file types. All three announcements come at the same time.
But nothing actually happens other than the announcement.
I'm running in a Limited User Account. Could that have anything to do with it? Why wouldn't the OS be able to make the changes? I'm glad it can't seem to do what it's threatening to do, but it's weird.
I feel just like a beta tester. Windows 10 is flaky.