Beacon held by player has a flashing texture on the bottom

Holding a Beacon in your hand and looking at the bottom of it shows a weird flashing texture where the glass and obsidian meet.

Steps to Reproduce:
1. Make a new Creative world.
2. Get a Beacon from the Creative inventory.
3. Switch to third person mode by pressing F5 twice and look down with the Beacon in hand.
4. Notice the flashing glass texture.