Are you forwarding using spanning-tree or helper addresses?
If you use ip forward-protocol spanning-tree, broadcasts will only be forwarded on interfaces that are part of a bridging group. Is bridging enabled?
Configurations night be useful here; how does the 4500 differ from the 3745? Which software versions are used on the respective routers?
"Exchanged broadcasts" is not a precise description. What kind of broadcasts, in particular? That is, what services or protocols are not working?