The impossible happened, code commented

initializeWorld = (\w -> do
		worldSetGravity w 0 (-1.0) 0
		worldSetERP w 0.2
		worldSetCFM w 1e-5
		worldSetContactMaxCorrectingVel w 0.9
		worldSetContactSurfaceLayer w 0.001
		worldSetAutoDisableFlag w 1),

these worldSet* functions are unsafe FFI calls. initializeWorld is Ptr Int -> IO ()

commenting this prevents this bug. this code is found in a top level declaration:

initiailLevel = Level {
 ...
}

of which contains the record for initializeWorld