I tried but still removes our tags:
Lets say we try this little test with a figure tag
It saves and its fine and dandy, check firefox inspector:
BUT when i try to edit the bloc again:
Aaaand its gone. Really frustrating, i tried to contain the class i need in other tags as a workaround but i swear no matter what combination i try, moodle always manages to delete important bits and make it not work.