Dog disappears, chests break, mobs invisible

Just upgraded to 1.2.15 and my game is going haywire. First, the game crashed and when I started again my dog disappeared. The next time I played some of my double chests were single chests. Then my sheep became invisible but I can still here them. Now monsters are becoming invisible. They can attack me but I can not see or attack them. Sometimes if I run away and look back I can see them again but then they disappear again.