I've also tried other forms of collision so it would change... see: I've tried overlapping, on collision... and even both. oh wait, I've tried even collision with solid (setting both sprites as solid, of course) and I couldn't even get the first collision in that case.
I've got to the extreme of trying platform behavior without gravity, speed etc to get the solid collision.
But in the end, megaman (wich is a random sprite I've picked just to figure how to make a loop) always ended up going out of the loop in a different way. yes, even with overlapping, wich made him go out on the funniest way possible:
overlapping with the loop slowly until he finnaly loses contact with it and fly away.
and about the angle issue pointed by deadeye: I've noted it even before I posted, because I did all I could to get outta the problem, but, as mentioned above, overlapping also takes him out, and I can clearly see that the first wall he touches is mostly the right one, since he usually's NOT touching the "ground", and he goes out even when he touches the right wall only.
(by "right" I don't mean direction, I mean the wall he must touch to change direction)
so, I got your point deadeye, since I suspected about it too. and I still suspect a bit, since I've separated the bars and left only 4 of them, and he moved like a square, and worked well.
but, for the reasons mentioned before, I'm afraid it isn't the case.
edit: maybe I should upload a pic. should I make an account in photobucket or stuff like that, or is there another way?