Brew stand

If you try to build a tnt cannon with brewing stands for the projektiles they will won't throw away while the rest of the tnt in the water explodes and they just will explode on top of the brewing stands. Asking why using a brewing stand out of a normal block? Thats easy: if the tnt gets ignited it normaly (like in the pc edition) drops a bit into the brewing stand what changes the way the tnt fly's.