Mobs spawn in blocks

I will regularly find mobs (only zombies) that have spawned inside of a block. They are stuck there until until you hit them at which time they come out of the ground and move freely. Also have the issue of iron golemns doing the same thing, though I only shoot them with arrows and they never get unstuck. Ideas? Playing on realms PC edition. Oh, not to mention these zombies appear in a little secured area...