This is the return of an old bug, which had been fixed several betas ago. Shortcuts such as paste and match formatting (Ctrl-Shift-V) and italicise (Ctrl-I) are not working in Inspector comments or footnotes.
I reported this for a much earlier beta, and it was fixed, but now it's back. (I'm using the hiDPI 64-bit version of RC7, in case that's relevant.)
Thank you, this has been filed. There has been some recent work with the popup comment boxes which I'm guessing negatively affected this. Most of the shortcuts seem to be working in comments loaded in the inspector but not in the popover. I'm checking this right now on a slightly newer build than RC7, so it may have that bit fixed from the public release, but if you happen to have only checked this in popovers, see if opening the comments & footnotes inspector pane helps--you may be able to apply the italics, etc. there for the time being.