system-config-network-1.5.93-2.fc10 saves gateway address for both a mask field It happens not all the time but quite often. system-config-network-1.5.93-2.fc10
I found the combination to reproduce it open system-config-network open device profile choose Hardware Device Tab go back to general Subnet mask is now equal to the Default gateway address.
*** This bug has been marked as a duplicate of bug 469434 ***