Invisible mobs.

Put the summary of the bug you're having here

What I expected to happen was...:
After Death, upon respawn mobs close to the player are not visible.

What actually happened was...:
You should be able to clearly see the mob. This is not the case.

Steps to Reproduce:
1 - Enter new game (in this case survival flat-world with creative as default so user can switch game modes) 
2 - Allow yourself to be killed
3 - Click respawn and note your under attack from an invisible mob. Seems to affect only mobs close to the player as mobs at a distance are visible. Affects all mobs by appearance. 

***This can also be proven by doing the following

1 - Enter new game in creative (I used flatworld)

2 - Build an enclosed area around your spawn location.

3 - Ensure no mobs are this area (thus preventing any mobs from being inside)

4 - Change your gamemode to survival at this time.  -  You will be attacked shortly after or immediately by an invisible mob.  This mob will kill you. You can not hit it or it appears you can not.

I have provided a few screenshots below and can provide more including a video if t will help.

IMPORTANT - I noticed if you wait a few moments after death while watching the respawn screen you will suddenly see the mob which killed you appear and walk away.