I don't mean to always pick on Google (yeah, pick on someone your own size...), but I love it and use it so much that any small problem becomes really annoying.
Since I've installed the Better Gmail 2 Firefox extension, I've become accustomed to using the keyboard to read my emails. Most keys also work without the extension, but I love my 'l' shortcut to label conversations. Anyway (see how much I love Gmail?), the bug I'm talking about is for the starring key, or 's'. Every key that applies to emails work the same way, except for this one. If you try to remove the current label ('y'), it works on all the conversations you've selected. If you try to delete an email ('#') or mark it as spam ('!'), it works on the conversations you've selected. Starring, however, works on the conversation the pointer is pointing to. That is, you cannot star multiple emails at the same time; you have to star, move down ('j'), star, move down, and repeat.
Again, I wish Google would just follow the rules, instead of having different functions operate differently.