I recently upgraded from 12.04LTS 64-bit to 14.04LTS 64-bit. My system is a desktop using the NVIDIA GeForce 210 card connected to two identical Samsung SMS23A350H monitors via HDMI cables. I'm currently using the NVIDIA binary driver - version 331.113 from nvidia-331 (proprietary, tested). The system works fine until the lock screen activates. When that happens the main monitor blanks correctly but the second goes into a state where the video is torn (like loss of H-Sync on old TVs) and occasionally flashes on and off. I leave the system on all the time so this is particularly annoying at night.
In short the lock screen (power saver) mode does not seem to be correctly blanking the second monitor.
Does anyone know a fix for this?