I narrowed down a problem on Firmware 1.21. It is most likely a memory overwrite problem when entering a MAC Address in the "Manual Internet Connection Setup" form.
I reported the details to D-Link support, and all I got back was "Have you tried upgrading your firmware?" Obviously this person has never been a programmer or a tester, and doesn't understand how memory overwrite bugs can cause unpredictable problems, including any of the problems being reported in this forum. If the bug isn't fixed, upgrading to a new version of the firmware will just make problems show up elsewhere where they are harder to track down or reproduce.
So I figured I'd come here and ask: For all the folks that are having odd problems with the DIR-655 that D-Link can't seem to reproduce or fix, how many of you are using a cloned MAC address?