Are you sure that all the clients have as default gateway the IP addresses of the bridge? of course the default gateway for the subnet 10.74.11.0/24 has to be 10.74.11.50 and the one for 10.74.53.0/24 has to be 10.74.53.54.
In any case the next release of Zeroshell has support for multiple interfaces for the captive portal. So you do not need to create a bridge.
Regards
Fulvio