There is a case where the relay agent could receive a request where the downstream node added Option 82 information without also adding a giaddr (giaddr of 0). In this case the default behavior is for the router to drop the DHCP request. This behavior is in line with the RFC.
The 7210 SAS supports a command trusted, which allows the router to forward the DHCP request even if it receives one with a giaddr of 0 and Option 82 information attached. This could occur with older access equipment. In this case the relay agent would modify the request's giaddr to be equal to the ingress interface. This only makes sense when the action in the information option is keep, and the service is IES or VPRN. In the case where the Option 82 information gets replaced by the relay agent, either through explicit configuration or the VPLS DHCP Relay case, the original Option 82 information is lost, and the reason for enabling the trusted option is lost.