It could be a firmware bug, or it could be something else bugging out. If the router hasn't been factory reset and it's been through a few firmware upgrades, try resetting it to factory defaults. Take note of any custom settings you have, so you can go in and manually re-configure the router. I would avoid importing a backed up config file in case the config turns out to be the problem, but it doesn't hurt to download a copy of your config now.
Give that a try. Others might have some more ideas.