launcher background shows black bar when on right hand screen

[Colin Law]

Using unity-2d 5.7.0-0ubuntu1 with a laptop plus external monitor.
If I position the external monitor to the right of the laptop the launcher appears on the external monitor (so in the centre of the virtual desktop), which is itself not a problem, I understand this will soon be selectable, but the launcher background shows a vertical black bar at the right hand side, and I think the left hand side of the launcher background is the right hand edge of the wallpaper, though not certain of this.

See attached image.

If I position the external monitor on the left of the laptop the launcher still appears on the external monitor (but now at left side of virtual desktop) and the background behind the launcher is the desktop background as it should be.

Screen resolutions are
laptop: 1280x800
external: 1280x1024

[Albert Astals Cid (aacid)]

Can you try this with Unity 5.10?

[Colin Law (colin-law)]

I can confirm that I still see it with unity-2d 5.10.0-0ubuntu1

I can now position the launcher on either screen of course, but when on right hand screen the background behind the launcher is still as shown in the earlier attachment.

[Colin Law (colin-law)]

The effect varies with the size of the image used as the background, it is not noticeable on the default background as the black bar is not visible in this case and the background has no obvious pattern. I am pretty sure the fundamental problem is that the background behind the launcher is coming from the right hand side of the left hand screen rather then the left hand side of the right screen (or something like that anyway). It can be clearly seen on the well patterned standard backgrounds such as the psychedelic orange and blue one which I think is the side of a boat.

[Colin Law (colin-law)]

Following further investigation I find that this is a side effect of the workaround for bug #788607 "gnome terminal hiding other windows and screensaver with dual screens". The workaround for that is to disable compositing, which causes the effect I have reported here. I will mark this bug as invalid.