13.1 network up but not working after router reset

Hi All.
I have a weird problem.
I have a fairly simple network setup:
Router (ISP provided):

In that network I have two windows PCs (via wifi), one openSUSE 12.3 x64 KDE SC laptop and one openSUSE 13.1 x64 KDE SC HP server both via UTP CAT 5 cable.
The server is the only PC configured with a static ip and network is handled by Network Manager (please don’t rant).
Everything works fine until the time I reset (power off/on) the router which is need about once every two days because of dynamic IPs being blocked by spamhaus (not my fault).
Then even though the server seems to have a running connection, the connection is actually lost and I have to unplug the UTP cable for a couple of seconds, disable networking and enable it again to have the network up and running again.

The other openSUSE PC and windows PCs work fine (with DHCP leased IPs).

Do you have any clue what might be the reason for the server not resetting the network connection after rebooting the router?

Thank you in advance

PS. The same thing happened with the server with openSUSE 12.3

Do you use for that fixed (non-DHCP) IP address one out of a range that is reserved for that purpose in the router?