What I expected to happen was...:
If I break a torch on the wall, the torch should break while the block behind should stay.

What actually happened was...:
On rare occassions the block behind the torch would break too (if the block would be mineable by hand it drops as item, else it vanishes, might depend on the tool you wield)

Steps to Reproduce:
1. Happened on a 1.4.2 multiplayer server, doesn't seem to occurr in singleplayer, can't tell if it's caused by main client or from plugins.
2. Place a torch or any other instant breakable item (redstone torch, netherwart, didn't see it happen with others yet) on a block (stonebrick, grass, dirt, stone, soulsand)
3. Break the torch in a way that the block behind/beneath is in thecrosshair as soon teh torch comes off.
4. Since it's a rare occassion it might take a while (after logging in I harvested almost 3 stacks of netherwarts to have it happen once)