Upon upgrading the firmware from 3.12 to 3.13, I found that my 6in4 tunnel no longer worked. (It's labelled "IPv6 in IPv4 Tunnel" in 3.12, and something slightly different in 3.13). Oddly, the DIR-615 Web interface seemed to keep dropping my setting for "Local IPv6 Address". I also tried configuring a 6to4 tunnel. There weren't any glitches with the settings there. However, in both cases, IPv6 remained completely inactive. I couldn't even ping6 the router via the link-local address.
I decided to roll back to 3.12.