Explosions Bypasses Water.

While using a TnT cannon I had made in single player just for fun, I noticed that the redstone and blocks that held the tnt would explode even with water protecting the blocks. Inspecting the cannon further, it seems only the cannon's left and right blocks were destroyed. Once I tested again, the back exploded. However, in the snapshots/versions prior to this, I can use the same TnT cannon just fine. The image file named 1.7 is the results of the cannon and how the cannon was built in 1.7.4, and the file named 1.8 is the cannon and it's results AGAIN in Snapshot 14w10c. Any other information needed, just ask and state specific things you need to know!