Not quite certain what the cause is but I've had two or three times now where the U2713HM begins flickering. I thought perhaps something was wrong with the MacBook Pro that I had connected to it but I disconnected it from the DP to MiniDP cable. Likewise, I disconnected the desktop workstation connected through DVI-D cable provided with the monitor.
It's more worrisome that when the monitor gets this way that it stays this way (the floating self diagnostic has the lines as well) for a few days and then goes away.
Is there a clocking issue or is this just a faulty unit?