The attached image shows the range of some common TNT cannons compared in the latest release and the latest snapshot. The cannon in which the TNT projectiles rest on a ladder has not changed. The other two cannons have the TNT resting on a slab and a fence, and their range has been reduced dramatically in the snapshot. These cannons each used three charges (TNT used to launch the projectiles) and the water in them was not moving, so no TNT was pushed by it in the snapshot.

It seems that the way blocks obstruct explosion energy has changed in such a way that slabs and fences obstruct much more of the blast than they are supposed to.