I'm not sure why that would be happening, but you can program DHCP relay into each of the VLAN interfaces. This is with the assumption that you are using VLAN interfaces and not just VLANs.
int the given interface that you want to relay DHCP requests, issue "ip dhcp relay destination X.X.X.X" statement.
The interface will relay all of the DHCP requests seen on that interface to the X.X.X.X address.
This will happen even if DHCP is running on the switch.
Funny thing is, I tried that yesterday. It would take hours of testing to finally figure out that I forgot to "activate" the scope on my dhcp server.