This occurs to you in SSP too?
SMP is just the lagg causing it.
Upside down does the same, Etho has accoutered the problem too: /watch?v=1qcxJClC99w
I also confirm this. It also happens that if you stare to the sky, it gets darker when hovering over a item
Yes, this also is a bug to me. And quite annoying.
Confirmed, only when you place a TNT block right next to a Block of Redstone, it will trigger.