One of our two d2g's had this issue, even after multiple reboots. It was not router related but seemed to be fixed by removing the motorola wifi-toggle widget from the homescreen. The second phone has yet to bug out like the first one did, even though it's on the stock (2.4.29) firmware. I also updated the troubled phone to 2.4.330 before giving it a really thorough test, so that may have helped, too.
Router settings are G/N mixed, 2.4GHz only, wpa2/AES and, to be clear, both phones are working perfectly now.
I recommend using AES-only mode on your router rather than TKIP/AES. TKIP is a security vulnerability in WPA/WPA2, as I understand.