Some portal blocks will render the other side. This may or may not be related to the fact that I made a larger portal. When your head is inside them, you can see the exterior. F3+T fixed the problem. I was not using texture packs.

What I expected to happen:
I would see them similarly to the other ones, only showing the front side and not showing the placement of the exterior of the portal when inside.

What actually happened:
I saw the other side when looking at it, and saw where the exterior was.

Steps to reproduce:
1. Make a larger portal.
2. Light it
3. Occasionally they may render like they did prior to 1.7.2 (or whatever snapshot it was).