Static route over DHCP problem !

We have a site with 2 gateways.
Let''s say 10.0.0.1 and 10.0.0.2. For one application we have set this staic
rout in DHCP: 10.20.20.100 255.255.255.255 10.0.0.1
All other traffice uses 10.0.0.2 as gateway.
This worked fine...but now the 10.0.0.1 gateway is obsolete, and we should
ony have one.
I remove the static route from DHCP, and hope that client should delete the
route information. But it does not !
I have delete all leases, rebooted clients, IPCONFIG /renew...but after a
boot it's back again!
The lease time was 3 days, but now set to 20 minutes.
I do not understand why the route get put in again!