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
Duplicate of MC-30796, please use the search function to see if your bug has already been submitted. Currently over 57% of tickets are being resolved as duplicate.