fireballs/witherskulls stop breaking blocks

I suspect this happens because fireballs explode in position where they last ticked and not directly at point of impact and because they accelerate up to almost 1.9 blocks per tick and their block breaking range is 1.7(3) blocks they can actually colide with a block and explode so that it is outside of explosion range, try moving the wall 1 block further and it should be destroyed again. With wither skulls its the same situation except they accelerate to much higher speeds, maybe even infinite, but the principle is the same.