Affects Version/s: Minecraft 1.8, Minecraft 1.8.1-pre3
Fix Version/s: None
Silk Touch doesn't works when you mine a block with any tool with zero durability and it breaks.
It works before 1.8 and I can confirm it in 1.7.
I made a short video with bug demonstration (sorry, it isn't english but you can see how it works even if it's obvious):