To be fair, the code base for this site is confusing as hell and Blink's ont a web developer. It's a pretty minor thing and I would probably solve it by disabling avatar uploads on signup entirely, were it up to me. In fact, I'm going to go see if I can do that
It will lead to less confusion certainly.
Edit: apparently, they are the same function. It simply doesn't autoresize signup uploads while it does profile uploads. Oh well.