I have a DIR-825 connected to the cable modem, TiVo and a desktop, then a DAP-1522 which is wired to another desktop and a 360. Both the DIR and the DAP are running the latest firmware.
Whenever someone starts to use the wired desktop after a period of inactivity, all wireless devices (everything on the DAP-1522) loses connectivity, lasts for 30-60 seconds, then everything comes back online. Everything remains fine until the wired desktop is idle for a while and then someone uses it again, then problem repeats. But it is also not universal- it doesn't always knock the wireless offline, but often does.
I am not sure if this is related to the DNS Relay issue or not. My option to uncheck "Enable DNS Relay" is disabled.