I'm having the same issue. Except I cannot access any external sites after a reboot also. Changing the default to something else and then back to the gateway group fixes all flow issues.
The other option I see of doing is setting the gateway group under lan rules, and setting the routing default gateway to automatic. This breaks "static routes", so additional rules would need to be made for a few static routes I need.
I experienced this issue under the RC and now with a fresh install of 2.4.4-RELEASE-p1.