I (and some other users) experienced big problems which are probably realted to yours ( https://bugs.launchpad.net/ubuntu/+source/linux/+bug/661294 ).
In my case the exchange of the Realtek OnBoard NIC with an Intel NIC (Intel 82541PI Chip) also solved all problems which seemed mysteriuous before.
I (and some other users) experienced big problems which are probably realted to yours ( https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/661294 ).
In my case the exchange of the Realtek OnBoard NIC with an Intel NIC (Intel 82541PI Chip) also solved all problems which seemed mysteriuous before.