With the release of Minecraft 1.3.1, there now a small chance that a zombie pigman will spawn next to a nether portal in the overworld. This has already happened to me twice in the space of a few hours.
Is there any way to prevent this from happening?
Best Answer
So far the only way to prevent pigmen from spawning is to turn off your Nether portal. You can do that by dumping water on the inside of the portal frame using a bucket or dispenser with a full bucket inside. Lighting the portal doesn't stop the pigmen from spawning, because I have a very well lit portal and one still spawned nearby. According to this answer, zombie pigmen spawn inside the portal so you can't put a transparent block to prevent spawning either.