I created a new world to test out the 14w30b snapshot and began flying around in creative just to explore and see how the world loaded. All was going well for a few minutes until the game crashed.

The issue it came up with was a tesselating block model, specifically for a piece of bedrock near my spawn point - I was up about 50 blocks flying around at the time.

I loaded the world in again and continued exploring, but only a minute later the game crashed again, once more for a tesselating block model - this time on a piece of tall grass.

I tried to send the report, but the launcher message said it thinks the game may be modded, which it's not, so it wouldn't let me send the crash report properly. Both crashes happened when I was playing on a brand new world, flying around in creative mode, on normal difficulty.

Edit: Just got the crash again, this time for a grass block. Again, the launcher thinks my game is modded.