Collisons outside window

Hello everyone, I'm kind of new here, I'm making a 2d scrolling puzzle platformer, I've got a weird problem.
I've got moving platforms and whatnot, and I'm designing my levels in a non-linear fahion, so you have to do a bit of backtracking. The problem is, when I select Handle background colisions when outside of window, all colisions work well except that of the player object, moving platforms and enemies colide ok, but the character object just falls straight through the ground as soon as he leaves an area wich is a bit larger than the game window( this is probably the weirdest part).
Needless to say, the opposite happens when I deselect it, so my player works okay but platforms stop colliding and fly off the game screen as soon as they leave the application window.
I'm using a custom movement for my player and obstacle backdrops for most of the level. Any help would be greatly appreciated as I'm actually prototyping for a work application and I'm on kind of a tight deadline.
Thanks in advance!