well i found something wired but same consept on 1.4.2 if you take oak leaves and you click on a birch tree (same texture different color) then it either glitches and removes the oak leaves in first slot or goes derp xD so mojang needs to iron out more bugs!
ACTUALLY THIS IS WRONG
**What actually happens:
And pull the lever, the tnt goes up and duplicates into 2 pieces of tnt only powering one.
WHAT REALLY REALLY HAPPENS:
for one you don't even need the torch up at the top just the lever and i will explain what happen's in more detail:
When you pull the lever the piston and tnt get powered at the same time and minecraft handle's both at the same time resulting in a tnt blcok being activated and a tnt block being pushed thus make a glitched tnt. When i think abought it then i wonder why the ghost tnt is not a real block.
i actualy have a bit of a showoff on this bug http://youtu.be/FTcL0HnY24U (not really the same thing but it's still the bug in a way)
CubeTheThird is correct
my computer specs are the same as yours and I can't seem to recreat this bug under the same sercumstances
"Cannot reproduce in 1.7.4"
Are you sure? i'm able to reproduce in 1.7.4 in all 3 gamemdoes