Graphical glitches when using OpenGL compositor in KDE

[Knowbody]

I've been able to install the Displaylink 1.1.62 drivers on my OS, which is:
* LMDE base install
* Debian sid repositories
* KDE Plasma with SDDM
* Intel Linux 1.4.0 graphics drivers

The hardware is:
* Toshiba Tecra 2 Z50-A
* i7-6500U + Integrated GPU
* Nvidia GT730M - which I haven't installed drivers for it and it isn't being used.
* Targus ACP70AU USB 3.0 dock which has the Displaylink outputs I'm using

I copied and pasted some of the commands from this script to install it:
http://displaylink.org/forum/showthread.php?t=64235

So anyway, I have a monitor connected to the HDMI port of the laptop itself, and a monitor connected to the HDMI port of the dock, and they're both working.

However, if I'm using OpenGL 2.0 or 3.0 as the compositor for KDE, I get some graphical glitches (copies of the mouse cursor left behind, etc), which does not happen if I use Xrender as the compositor, and also doesn't happen if I'm not using the Displaylink output and I am using OpenGL.