MR1100 ethernet port dies when charger connected

This is a strange one and it's driving me nuts.

Started about 3 months ago (just after the warranty expired, natch):

The ethernet port dies whenever the charger is connected.

To use the ethernet port I have to:

1) disconnect the charger cable

2) shut down the Nighthawk

3) wait a little while (won't start back up immediately)

4) fire up the Nighthawk

After which it works just fine until I plug the charger cable back in (which I kinda have to do sooner or later).

Have tried everything I can find suggested, in particular firmware is uptodate and I've disabled timeout on the port but nothing seems to work.

Any ideas?

Thanks.