Glitchy lines between blocks

I was playing the snapshot and I looked closely at blocks and I saw lines between them. I tried this in both Fancy Graphics and Fast Graphics and they still showed. I don't now if it's just my computer or not. Also, this does not happen for me in Minecraft 1.4.7.

NOTE TO MODS WHO GET MAD AT DUPLICATES: I searched "glitchy lines" and nothing came up that had to do with my issue