When the torch is placed at "a" (on the picture attached) it jumps to "b". Not totally sure whether this started immediately or set in.
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Confirmed in the 1.4.3 prerelease. On a private SMP server, the torch briefly appears in the correct location, then reappears on a different surface. Placing on the ground is the hardest - this will only work when all four other surfaces around the torch are unsuitable.
I've not tested on single player.
Duplicate of/related to MC-1731