Display bugs

I built an underground village which all the beds are in a huge room. When the night comes and villagers go to sleep, they act like they get onto the beds, rapidly move apart from the beds (with sleeping position) and disappear. Next day, they will appear again and working as usual. 

Besides, if mod farm (mine is zombie pigman farm) accumulated mod for a period of time and it reached certain number, some of the pigmans will be shown like standing outside the killing chamber. when I start to kill those in the chamber, the images of zombie pigmen outside the chamber will come back to the chamber and get killed by me.

Another one is I found that sometime glass block will be totally invisible instead of shown the light blue pixel.