I am an avid user of Windows suspend/standby, and I think there is a Bug in MIDI Mixer. Whenver I return from sleep, changing any of the sliders etc. doesn't work anymore. Restarting MIDI Mixer fixes this. I am assuming MIDI Mixer and the MIDI device lose communications during the standby and don't re-establish it. Probably could be fixed by subscribing to the sleep(return) event and then just triggering device load anew or something like that.
Lemme know if you need any additional information!