I haven't used Medium, so I can't speak to it, but in my experience the most frustrating instance of this behavior is from Stack Overflow. Keybindings such as `Ctrl`+`k` and `Ctrl`+`b`, which are native to OS X, behave completely unexpectedly in Stack Overflow textareas, to the extent that I sometimes just give up and compose my text in an external editor.
I've grown accustomed to writing longer comments or posts in an external editor, simply because I've too frequently experienced browser crashes, or an inadvertent (or absent-minded) screen refresh. Alt-backspace is my worst offender, as I use that ALL the time in the shell for text editing, whereas in a browser it navigates backwards.
Worst of all, I can't seem to find a way to alter the keybinds, or (more importantly) the mouse-5-means-go-back gesture.
