Comment 4 for bug 1181622

Alexandre, I believe this is due to e1000e driver power management bug that was present in the 3.8 (raring) kernel. Basically, the ethernet card couldn't detect carrier signal if it was on deep sleep state (e.g., the laptop was on battery, not on AC).

I've uploaded a test kernel here that contains the fix for this e1000e issue: http://people.canonical.com/~henrix/e1000e-pm-bug/

The fix is already in Raring master-next branch and should be released soon.