I have come across this in Moodle 2.2.2 using Chrome & Safari (client didn't test Firefox) on a Mac.
This is happening to an admin role on the site, however, as an admin myself, I have no problem and am able to see the buttons for both images & embedded media.
I have seen sporadic forum posts about this being related to forums or MCQ, but it seems to be happening in all areas where editing occors.
Any ideas?