Ok sorry i forgot to say too that this is just a alpha so many things are soon to be fixed and added
...You do know that most if not all of us here know how to make a portal without cheating, right?
You also do know that the portal is not bugged at all right now, right?
are you sure you made the portal 5 blocks high and 4 wide? (3x2 Portal frame) that "bug" looks like what happens when you try to light a Nether portal with the wrong portal frame
Can I suggest you to please have a look at this Article, and watch it's video?
http://aether.wikia.com/wiki/Aether_Portal
Also, are you using 1.5.2 version or 1.5.1? And WHEN have you downloaded the mod?
I seriously need those informations if I ever get to help you. Thanks, and I'm waiting for your answer