Comment 4 for bug 1404147

This still happens in a fresh install of Ubuntu 15.04 with "NVIDIA binary driver - version 346.59 from nvidia-346 (proprietary, tested)" installed from the Ubuntu Additional Drivers tool.

Though I think I discovered a work-around. It seems like it only happens later if my monitor was plugged when the login screen was open. If I disconnect my monitor's HDMI cable, log out, log back in, and reconnect the monitor, it seems to work fine for that session so far.