multiple interfaces and subnet routing

I am running BM 3.7 SP3 on Netware 6 SP5. I have a default route set to my
ISP. I have a static route set for a xxx.xxx.0.0 net with a 255.255.0.0
mask set to point out a frame relay router port. I have taken some subnets
under the xxx.xxx.0.0 and given them static routes to another interface.
An example would be under xxx.xxx.0.0 xxx.xxx.0yy.0 with mask of
255.255.255.0 now points to the ISP interface. This has been working fine
for years.
I am now trying to take a host from the xxx.xxx.0.0 subnet and point it
out a different interface with a static route of xxx.xxx.x00.xxx. Default
mask for a host is 255.255.255.255. This will sometimes work for up to 40
minutes and then all routing for xxx.xxx.0.0 starts going out the default
route.
I am using a Cisco 3560 for a DMZ and a Nortel Accelar for my internal
routing. They seem to be ok. It looks like BM is the issue.
Any ideas out there?
Jerry