Thanks for looking at this! I see what you mean about the manual. Perhaps those aspects of the behavior have always been like that and I never noticed.
However, I still have the issue with double-click. I guess it essentially boils down to simply:
Double clicking on an image (in either lighttable or darkroom filmstrip) does not bring that image up in darkroom.
I have checked my mouse settings, all is normal there, and functions as it should with other programs. I made certain to not be running any other applications while testing. I have even re-installed dt 3.0 wondering if some setting got broken. I’ve also reset all my shortcuts to default.