recently i've ran into the same issue with ISR c2951-universalk9-mz.SPA.156-3.M3a. in dry essense , ISR doesnt unicast client's DISCOVERs (client's broadcast) to the configured on the arbitrary SVI helper if it works as the dhcp server for that vlan . But RELEASes (client's unicast to the ISR's SVI) are frowarded :|
