I had a bug in my game where the character would smash a block from underneath and keep jumping if shift was held.
This only happened on certain levels even thought the events were exactly the same on each level and i had put events in to counter this on every level.
The problem? One detector was behind the other! when it should have been in front!
(i have two head detectors you see)
Lucky i found that one out otherwise my game would never get done.
anyway just so you know objects don't work so well when behind another.