Animals and pigs zombies caught in the portal to the Nether

In your Nether portal, there are times where you try to take an animal or a pig zombie tries to come, the problem is that they stay in the portal bugeados and every time you leave or enter the second they come and go. It is a big problem because it can greatly affect the game if you want to take your dog or make a grabja in the Nether.
The worst thing is that I've lost animals through this and is a little uncomfortable knowing that now stay bug ...