This bug has appeared since sometime in the 1.9 snapshots and has since not been fixed, even in the latest snapshot. I'm not sure of the cause; it could be a problem that has something to do with resource packs and the new 1.9 sounds making them incompatible, but I'm not entirely sure.

Steps to reproduce:

1. Open up Minecraft PC.
2. Load or create a world.
3. Go back to the main menu.
4. Load that world again.
5. You should notice a visual glitch where blocks keep flashing all over the place.

Some images: