Subnet mask

We have some Windows 98 station. Sometime when we reboot the pc the subnet mask change without any reason. Our DHCP push 255.255.252.0 and on the Windows 98 station they it goes to 255.0.0.0. . So some network software stop working. The only workaround I found at this moment is to release/renew the IP address with winipcfg. We don?t have this issue on other Operating system (nt, 2000, xp). Thank you for your help.