Does anybody know where the new panel is supposed to appear? I get mixed results here (SC 4.5 RC2). Sometimes its on top and sometimes at the bottom, regardless if there were already one or not.
Whenever I've tried it, by default it has opened at the top of the screen. I'm running the same release as you. I'd avoid being specific about that, at least until the full 4.5 release. You could say that in 4.4 the top is the default - I think that is undeniable, though of course I could be wrong.
it tires to find a "free" screen edge, starting at the bottom. it then tries the top, then the left, then the right. it favors edges without panels touching them.
in the docs, though, it's probably enough to just say that it looks for an available screen edge to place it on.