What I was seeing was not ostensibly related to images in comments, but that's not to say it wasn't.
I am still seeing the last book added in Book details when I start or library switch to my Test library but it's fleeting (< 1 sec), and that is also true in 6.29 if I look closely enough, whereas it was 5-6 seconds in 7.0 → 7.5.1.
Bottom line: it's fixed
Apart from that: the keyboard navigable menu for the 21 Preference panels and a Live CSS panel I can read are much appreciated.
BR