U4919DW, KVM, usage, #3

I have this same issue. 

I have two U4919DW stacked on top of each other. I have two computers connected to the bottom monitor. I use the monitors in PBP and full screen mode. 

When switching USB, sometimes it switches successfully with me being able to use keyboard/mouse. However a lot of times when it switches, the keyboard is non-responsive and while the mouse is movable clicking does not work and scrolling the mouse wheel zooms windows in and out instead of scrolling up and down.

I noticed a firmware update available for the monitor and it mentions a "DDM" which I assume refers to Dell Display Manager. I am going to update firmware and see if it fixes it.