I haven't noticed this before, now it is really annoying, I don't think it was like that in the earlier versions. Blocks are just fine, it's just the 3D item models held in hand.
MC-19195
Item glitch. Pixels have space between.
Resolved
Duplicate
0
ShadedPL
(Unassigned)
Unconfirmed
Minecraft 1.6
Retrieved
I don't think this duplicates, blocks placed, and held by hand are rendered just fine, but items held in hand not.