If you reboot your router you must reset the proxy-arp because it doesn’t work… For example you must set arp to enabled and then to proxy-arp
There was the same problem with wireless interfaces 
I have the same problem with 2.8.8, and i must to check every time that the router reboot.
I see the change log on the 2.8.12 and it say:
*) fixed proxy-arp bug for wireless after reboot;
I will be upgrade the router box on this weekend and i tell you if the proxy-arp work.
Regards
M.
It doesn’t work. They fixed the bug only for wireless interface
What’s new in v2.8.13:
*) fixed problem - PPTP and PPPoE Windows client could disconnect
after about 15 minutes;
*) fixed bridge after reboot proxy-arp problem;
*) fixed crash when bridging fragmented VLAN packets;
I will try to install this version to fix that
Regards
M.
In v2.8.13, that is fixed.
John