Nether portal in new map!?

I just started a new map in creative and discovered a nether portal in the side of a mountain. It is already activated too! When I went in the portal, it led to the Nether, but there is what appears to be a chunk error or something. There is a big netherack (not netherbrick) wall with a huge whole in it. Other than that, the overworld and nether seem normal (so far).
Has anyone else seen this? Is this some sort of new update I missed? Is this a sign of Herobrine? (just kidding about the last one! )