I placed TNT down and then a redstone torch next to it, on the same level.

What I expected to happen was
TNT blows up.

What actually happened was
The TNT did not ignite, but when I triggered a block update of the torch (by placing another torch next to the original and diagonally from the TNT), it did ignite.

How to replicate
1) Place TNT on a flat area of ground
2) Place a redstone torch or block adjacent to the TNT - even on all 4 sides.
3) Note that the TNT does not ignite.
4) Place a torch next to the original(s) (but not a block, this will not trigger an update) Relative position to the TNT does not matter upon further testing
5) Note that the TNT now ignites.

How this should be fixed
Ensure that TNT receives block updates from redstone torches and blocks as soon as they are placed, instead of waiting for them to send one. This does not occur with doors or pistons, which are also redstone-activated device, so something has not been copied over.

Please test this, replicate it and assign to a mojangsta, as there appear to be no other issues like this.