Question : IP addresses released from 2 dhcp servers on different vlans on a cisco Switch 3560

Recently we have been experiencing different ip addresses being issued to clients on different vlans. We have 2 vlans on our cisco switch 3560 vlan 30 and vlan 50. Both these vlans have a seperate DHCP server configured. Now users on vlan 30 and 50 are getting ip's from both these dhcp servers probably on  FIFO based request.
I dont understand that why the request has to go the gateway of each vlan for dhcp request. The query for DHCP should first circulate in the local lan and only if the server is down it should go the gateway that is the switch.
I first used access list which i created using network assistance and restricted the entire vlan 50 subnet for the server which is residing on vlan 30 but the request would still come on the vlan 30 server probably because i created an ip access list instead of a TCP or UDP.
I then enabled DHCP snooping on the switch and enabled it only for vlan 30 and trusted the port which was connected to the dhcp server. It worked fine for a day and the very next day back to square one. Now i have enabled snooping for vlan 50 as well, but the dhcp server for vlan 50 cannot be trusted as it is connected to a different nortel switch.
Any other ways of keeping the dhcp servers restricted to their own vlans.

Answer : IP addresses released from 2 dhcp servers on different vlans on a cisco Switch 3560

>I dont understand that why the request has to go the gateway of each vlan for dhcp request. The query for DHCP should first circulate in the local lan and only if the server is down it should go the gateway that is the switch.

That's not how it works. The IP helper address will forward ALL DHCP requests (unless the forwarded traffic is changed) to the assigned address. What should be happening is that the local server's reply should be received first and that's the address it should be getting. I have seen similar situations where the local server was under a load and wasn't responding as quickly as it should have which results in the off-network server offering the address.

That said, the address being received should be for the network that the device is on. Do you have the scope correctly defined on the DHCP server?