It looks like this is a (surely quickly fixed) bug in the site itself.
They recently made some changes, allowing users to use a version of the live editor on Answers. A few of us had it enabled as beta testers, and it was to have gone live soon for all.
The entire formatting bar is gone now for me too (Mac OSX, 11.1, using the Safari browser), so the problems seems to happen with multiple systems.
Misha has reported it, but I have also sent in a report, and will followup on that.
Sorry about the problem.