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