I suspect this is not a Photoshop bug but that the OS may be at fault but if you want to file a bug report the official site for that is
As for restoring Photoshop Preferences: The need for that can arise occasionally and resetting them according to one’s likes can be (at least in part) automated.
Also it serves as a good reminder to regularly save one’s customised presets like Actions, Brushes, …
Goes to show that people have different perspectives. I really have problems seeing this as "invasive".
I have always considered it given that Photoshop takes over the file associations for all image file types. Why wouldn't it? I have never given that a second's thought - until now. I mean, if I install a simple thing like VLC player to watch videos, I kind of expect it to automatically open all video formats automatically.
Changing the relevant associations to something else is very quickly and easily done. If that's what you want.
PDF is a bit odd, though.
Actually, come to think of it, there are about 200 threads here where people see it as a serious problem when Photoshop does not take over file associations.
I called it 'invasive' because no app should automatically take over native OS associations without specific permission.
It is up to the end user to decide which app should open which file type, and change it as needed.
It is not up to software to summarily decide what is best for the end user.
Well, in any case - if Photoshop behaved the way you want, I can promise you there would be a tsunami of complaints the other way. I might join in.
I see no reason for it to hijack PDFs. As for image files, if I change the associations, the app should be coded to respect my choice. Sure, it can offer me the option to switch back if I choose; any well-written app should.