I found some issue reports with the same issue in previous versions. But they all were marked as "fixed" but it's not:
I entered a nether portal, got teleported to nether but there I cannot leave the portal. I stuck in the purple animation, can interact with sourrounding blocks (set and remove them), throw items, but cannot collect them or leave the portal.
Here is a video: http://youtu.be/2r4uHc3CsOw
Here is the savegame: https://skydrive.live.com/redir?resid=C81227A545BDA7F4%21965
Linked issues
Comments 3
Destroy the obsidian from the portal. Without a diamond pickaxe, this takes 4 minutes and 20 seconds for each block and yields no obsidian blocks, that means you won't be able to return unless you have another portal or obsidian. Otherwise, the only way to get out is a little bit of cheating: Open to LAN > Allow Cheats: ON > Done, /gamemode 1 and then destroy the obsidian blocks, replace them when you're no longer stuck and light the portal again.
Yes, sounds like MC-2416 all over again. but it seems may very very rare bug now.
Both ways are not useable in my case, because I had no diamond pickaxe in shortcut bar, but only in the inventar which cannot be opend as long as you stand in the portal. Same with /gamemode 1. You are not able to chat in portals. And I also had no obsidian with me.
So I fixed it now by loading it in multiplayer and someone pushed me out of it.
That looks like normal portal behavior. If you remain standing in the portal after coming through, it doesn't just send you back and forth endlessly. You need to step completely out of the portal, then back into it in order for it to transport you back to the nether/overworld.