This was first observed on a Multiplayer Server, and checked on Singleplayer.

Steps to Reproduce
1. Load the Minecraft Client (1.5.1)
2. Select Singleplayer or Multiplayer, and any world on any mode.
3. Place a strip of Slabs of any type against Ice Blocks
4. Attempt to view the slabs through the Ice Blocks

Results:
When approaching Slabs that are against Ice the space between the slab and the ice block flickers for a few seconds.

2 Images Attached