One difference I notice upon closer examination in L3DEdit is that the other three levels, the poles either have a 3/4 block (with the bottom slab missing) or no solidity at all, whereas on HI123, they have a full block (invisible in all cases). However, changing this to a visible block and/or a 3/4 block in L3DEdit produces no change in L3DEdit, so I'm not sure if this is the actual cause.