So in my platformer, some strange thing was happening where my little Mario sprite would flash when moving and jumping. I just noticed he wasn't flashing, he was TELEPORTING -- to 0,0, to be exact, for a single frame at a time.
I took everyone's advice and made an invisible box be the real player with the sprite just set to its coordinates, but it seems the event tying them together isn't doing its job properly. Or, of course, I screwed something up.
EDIT: You'll also notice that the camera jumps around if you climb up the tiny hill to the right -- there's another invisible object set above Mario with the ScrollTo behavior, and apparently this teleporting issue affects that one as well.
Anyone wanna take a look?