In DemulShooterWindow.cs (and DemulShooterWindowX64.cs):

The line inside the function: private void ProcessRawInputMessage(IntPtr RawInputHandle)

was changed from:

if (Controller.isSourceOfRawInputMessage(RawInputHandle))

to:

if ((_UseSingleMouse && Configurator.GetInstance().PlayersSettings[0].DeviceName == Controller.DeviceName) || Controller.isSourceOfRawInputMessage(RawInputHandle))