To put it simply if you place a redstone torch on a block then a block of TNT on top of the block the torch is on, then proceed to place a block on top of the redstone torch it does not light the TNT as it should.
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Confirmed.

Duplicate of MC-266, please use the search function to see if your bug has already been submitted. Currently over 42% of tickets are being closed as duplicate.

Is this the same problem? http://imgur.com/ebKwoSs

Seems like it