Nether portals can now be created in parallel, immediately adjacent layers. Lighting portals in such a way will cause the portal tiles to become invisible(but still functioning). This only seems to effect tiles directly next to each other, not the entire portal.

IMO this seems like one of those bugs that people would like if left in, but that's up to you wonderful Mojang people

Example images (same ones in attachments):
http://i.imgur.com/wIUMN4s.png
http://i.imgur.com/b5oqlHh.jpg