I use the Professional edition too, and Windows resets my default image viewer and PDF viewer every now and then. Not sure if it's related to Windows updates, though. IIRC the resets are correlated more with one of those apps updating itself and Windows no longer trusting it with the defaults it had been previously granted.
Just speculation but perhaps the way the installers work makes it appear to Windows that the app was uninstalled first and then a new version is installed. If it looks like it was uninstalled then I can see why Windows might change the default.
Which feels quite amateurish and thus ridiculous for Microsoft. Like, they invent a new app store in Windows 10 and they still can't even be bothered to implement a working update routine that isn't infuriating to end users?
