I'm not sure it's a bug per se, but it's certainly an annoyance. When editing an answer in MO, I often hit C-b and C-k thiking (thanks to Emacs being hardwired to my ageing brain) that I will be going back one character or deleting forward until the end of line, respectively. This is how it works in this very text form, for instance; since I have instructed my Mac to use Emacs keybindings whenever possible. However, MO traps these keys and interprets C-b and C-k as "bold text" and "code", respectively.