Comment 3 for bug 1855792

daily test on hp 8200 elite sff (i5-2400, 8gb, nvidia quadro 600) again
I modified displays to match my setup (vertical, one screen above the other)
logged out to try using openbox for a quick test; logout of openbox
logged back into Lubuntu and

- my-top display had no wallpaper
- my-bottom display had the top-half of the default wallpaper

display orientation was saved in prior session (before logout & openbox session, then login now) but it has mucked up wallpaper now.

this is minor; though as a test I changed wallpaper & my top-display was still black (no-wallpaper), and my bottom-display had top of replacement wallpaper.

i played with Monitor.Settings and on adjusting displays and clicking 'Apply' I'd momentarily see the image correctly then top-display would go black & top-half of wallpaper would be re-drawn on bottom display.

From play (Monitor.Settings, esp. the Keep.monitors.attached option), I could correct & cause this issue to re-occur at almost predictable fashion..

I suspect from play this issue relates to http://launchpad.net/bugs/1814490, and an issue I've been wanting to raise upstream for a few weeks (but am unsure how to word..). Keep.monitors.attached??

What was obvious though - there was a bright blue line bottom of my-top monitor, being the top of the wallpaper (1910-boat-on-beach.png) that I suspect relates to issue, it shouldn't be there I believe (ie. slight overlap) occurs when Keep.monitors.attached is checked.. that seems to cause 1814490 & this to be mostly predictable..