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