This has just started happening with me on Ubuntu 14.04, after I updated my HWE stack. My laptop has an HDMI attached screen above it, so I use 1-vertical screens, 2 wide, which gives me a 2x2 set up.
When my screen locks, random windows will move themselves to a non-existent vertical screen below my laptop's screen.
To get them back, I start CCSM, choose General Options, then choose Desktop Size and change my vertical desktop size to 2, drag the windows back to a visible workspace, then change my vertical size back to 1. I can also use the methods described in this bug report.
If I leave my vertical size at 2, the windows still jump down randomly and I then have to add a third layer to my vertical desktop size to get them back, so the desktop size itself appears to be irrelevant.
This has just started happening with me on Ubuntu 14.04, after I updated my HWE stack. My laptop has an HDMI attached screen above it, so I use 1-vertical screens, 2 wide, which gives me a 2x2 set up.
When my screen locks, random windows will move themselves to a non-existent vertical screen below my laptop's screen.
To get them back, I start CCSM, choose General Options, then choose Desktop Size and change my vertical desktop size to 2, drag the windows back to a visible workspace, then change my vertical size back to 1. I can also use the methods described in this bug report.
If I leave my vertical size at 2, the windows still jump down randomly and I then have to add a third layer to my vertical desktop size to get them back, so the desktop size itself appears to be irrelevant.