UE3421WE - Audio Line-Out does not switch with KVM

I have two computers connected to my UE3421WE.

• Computer 1: Connected via USB-B + HDMI 1
• Computer 2: Connected via USB-C

The monitor is set to PbP mode - 50/50.

All USB-Periphery is connected via the monitor and the KVM. It between the two computers without any problems (with a set shortcut).

The monitor's audio line-out is giving me a headache though. It seems to be hardwired to computer 1 and will not switch over to computer to via the KVM. 

Does anyone have any ideas what could be causing this?