I've seen comments saying that this was fixed a long time ago, but I've randomly been able to do this pretty much since I've started playing (a few months ago, whatever version that was). I haven't tried it with the very latest version, but I was able to do it as of last version.

How high walls?

Standing up you can stab over=through a bit over waist high walls, that one is intended at least.

Yeah, short walls. Ok, it's a feature and not a bug! But basically every time I do it the other player responds with "WTF". Maybe this could be better documented or more obvious? No one expects this to happen to them.