When a torch is plased on the side of a block and the block is then powered, the torch on the side of the block will fall of is the block under the torch is a 'non-solid' block (such as air, slabs on the bottom half of the block, glowsonte, leaves, chests etc.) but functions as it should (as in it is powered off) when there is a sold block under it (such as grass, sandstone, soul-sand, fences etc.)

This but was then fixed in the 14w26c snapshot, I am assuming because of the code changed to fix the 'Floating Redstone torch' bug, however because I can not find a bug report or a 'fixed bug' statement on the subject I am making a not of it here for you guys to keep an eye on