Running Leap 42.1 and Plasma 5.4.3.
I connected the second monitor to the desktop, both running off the motherboard which has an integrated graphics card. One connected to VGA and one connected to DVI.
I booted up Leap and both monitors displayed the boot up sequence. The monitor on the right connected to DVI displayed the login screen and I logged on to the system.
However I noticed that the monitor connected to VGA was not accessible i.e. I could not drag the mouse to the VGA monitor and none of the applications would start in the VGA monitor.
I assumed that this was going be a driver problem as mentioned here: https://wiki.archlinux.org/index.php/Multihead#Xinerama
The integrated graphic card on the motherboard showed up as an intel 0042.
00:02.0 VGA compatible controller [0300]: Intel Corporation Core Processor Integrated Graphics Controller [8086:0042] (rev 12) (prog-if 00 [VGA controller])
Subsystem: ASUSTeK Computer Inc. Device [1043:8383]
There are no drivers available for this card.
I started the system settings display applet and had a look at the configuration.
I noticed that the applet showed the VGA display on the right and the DVI display on the left where as physically the VGA monitor was on the left and the DVI monitor was on the right.
I then discovered that it was possible to drag and drop the monitor icons in the display applet so I swapped them around so the display in the applet reflected the physical location of the screens.
I applied the change and the VGA monitor became accessible. I could drag the mouse and applications between the screens.
Obviously the physical location of the screens makes a difference. I have no idea why.