Am I right in assuming you expect to bounce off the ceilings and floors when holding the Z button down? Because no, that's not meant to happen. It's a good idea in theory (making the game pinball-esque), but I'll probably use it in a later level. If you mean simply jumping and landing stops your speed, that shouldn't really happen. Will take in mind the animation though.
Good point. Fixed.
There actually is a ceiling sensor already. I think it's something to do with the left/right sensors pushing everything upwards and outwards though, including into the background. I'll have another look at this. Thanks for the comments!