Mobs are moving very slowly

This bug seems to have several problems, one of the main problems being the mobs moving very slowly.  some animations for the mobs still work, but the mobs are moving very little and are mostly just staying in place.  When you try to hurt a mob or spawn a new mob with a spawn egg, it takes a long time for this to happen.  I have also noticed that when a block under something like tall grass or a fern is destroyed,  the plant on top is not destroyed along with the block.  When the trunk of a tree is destroyed, the leaves do not disappear.  I also noticed one time after loading the word that after flying about 40 blocks away from the spawn point, I immediately reappeared back where I was before.  However, this problem stopped occurring.  I have played on this world before and not noticed any problems with it before.  Walking, placing blocks, and destroying blocks takes the normal amount of time, although I have noticed that the top half of a bed takes a while to load when it is placed.  I did try to open another world, which turned out fine.