This always happens when I try Adding TNT surrounded by bedrock. Every time there ends up being a huge ditch under the area, even when I add a roof. 

Steps to Reproduce

1. Build a "box" out of bedrock with a 3x3x3 interior with a hole in the roof
2. Make sure there are no blocks adjacent to the box
3. Fill the box with TNT (at least one layer)
4. Set off the TNT, plug hole before it explodes

Observed Results
Some of the TNT explodes outside the box, destroying nearby blocks

Expected Results
Explosion is contained by the bedrock box

Additional Notes
The TNT only seems to glitch through the "North" wall.
If you put an additional layer of any kind of blocks, even ones with minimal blast resistance, covering the "North" wall of the box, the explosion is contained.

_{note that during the video there was no roof but later on I re-did it with a roof and got the same results}