Comment 93 for bug 5364

i resolved my problem.
The guilty was nm-connection-editor who didn't save the gateway configuration, even if i wrote it.

Workaround:
- open gconf-editor
- search in /system/networking/connections the problematic connections ( 8, in my case)
- open the voice ipv4
- in addresses, i replaced the last 0 with the integer conversion of my gateway ip

For ip to integer you can see:
http://www.arachnoid.com/linux/NetworkManager/