I noticed this yesterday but forgot about it until now.

Anyways, I joined the SK beta server and before I joined a team I pressed F1 to see who was on which team (Because they were equal) to better help me make my choice. Well, after I pressed F1 again the join team menu disappeared. I even pressed Esc, went to 'Change Team' but no result. In the end I had to leave the server and rejoin for it to work.

Can anybody else confirm this?

It works for me, but when I tried it, there isn't anyone in the server.