Two things, not bugs exactly, but ways in which something is not providing what it was apparently meant to.
First, on page for a group, in the Visit My Group sidebar, the list of groups and forums with messages goes out of date when you read them and does not update on the page, even with reloads, for a considerable time. I haven't actually timed it, so I don't know.
Second, on the My Groups, by default it shows you ALL groups, including Premium and Free. That means it shows you EVERYTHING--all new works. Or you can select an individual group, but then you have to look again for each group you are in (except Premium and Free, which between them represent EVERYTHING, or EVERYTHING that is not in a private group. There is no way to select mutiple groups, or ALL-BUT-PREMIUM-AND-FREE, which are, in a sense, the 'base' groups, the two parts of the universal set.
More grist for my thinking on groups, but for now adding 'chosen groups EXCLUDING Premium and Free' would probably come closer to what most users would hope to find.
IMO.