WHOOPS

Its happen because...

Glowstone and redstone block emits light... if there is literally 0 light you will die (gravel sufffocation, void suffocation)
Not sure on tnt though
yet leaeve dont emit light BUT light goes through leaves SO you dont die

Its a lighting glitch what is your smooth lighting setting?

I think this is a crowding glitch because you normally cant spawn 2 mobs on 1 block and so the mobs look like there going throught the fence and then get drawedback to the barn (i thinks its a game logic clash)

I would reccomend allow minecraft to use more memory with magic launcher but i dont believe you as i had bout 60fps on the old smooth lighting but i have a small fps decrease of 15fps

Happens also in creative and some times the number gets removed and also happens with 1 character or the underscore in the console yet it only cycles grey in the console

Direct relation to MC-11033 ive seen those flikering items I would now accept this as a duplicate of MC-11033