I see this happen somewhat often using FireFox too. As you say, the buttons are ALL missing,
and a reload takes care of it. I checked the source once on these but it looked fine: the CSS
for the buttons was all there. They just didn't show up.
I've also had situations where the front page says there are replies, but when I click the
link I don't see any replies. Then if I reload, the replies appear! This happens more
rarely, but it's happened more than once.
At first I thought it was because I was using the greasemonkey add-on to distinguish between
read and unread comments, but I've since turned that off and I still see both of these