Background Input for WGInput controllers not working

[grazy9999]

With Dolphin Release 5.0-16793 it is possible to use a controller as a WGInput device. This allows e.g. more than 4 Xbox One controllers to be recognized by Dolphin and linked to controller slots.     
My problem now is that the option "Background Input" under Controller settings      does not seem to work with WGInput devices.
When I use controllers as XInput devices, I can operate 2 Dolphin instances in parallel even if only one of the two windows is in focus/foreground. As soon as I change the controller to WGInput the parallel operation does not work anymore.

Does anyone know a solution for this?
I want to work with 8 controllers on several different dolphin instances in parallel.

Thanks for any advice
grazy