Comment # 2 on bug 65810 from Alexandre Detiste

I have the same after playing SpaceChem(game using Mono) on Steam.
It goes away after stopping Steam.

xwininfo: Window id: 0x4a00073 (has no name)

  Absolute upper-left X:  0
  Absolute upper-left Y:  0
  Relative upper-left X:  0
  Relative upper-left Y:  0
  Width: 64
  Height: 24
  Depth: 24
  Visual: 0x216
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x4a00072 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: yes
  Map State: IsViewable
  Override Redirect State: yes
  Corners:  +0+0  -960+0  -960-744  +0-744
  -geometry 64x24+0+0