Why do you end up stepping on a shroom if you are autoing it and lose vision of it?

I'm wondering why this happens, if you lose vision of a shroom you're trying to kill, you end walking towards it.

It's really annoying, especially with melee champions because they don't have time to stop walking before stepping on it.

Sorry if this is on the wrong board, I don't really know if this is a bug or not or what.