We use the kln-90b in the 1900 and it is definately not a Garmin unit.
Our SOP's state for us to select the next waypoint, allbeit a hold or a fly over waypoint in the hilighted field in fpl0 or on the super nav 5 page so that when you commence the mapp, ie: climb and start the turn- if required then you can go direct to/ goto, (however you want to say it) the next waypoint in the missed approach as the kln90b does not provide waypoint sequencing onto the mapp.
Once you have done that then you have an active waypoint so selecting obs mode will allow you to set the correct course to be flown on the mapp.
Having it hilighted makes the process easier to follow when you are low to the ground and in the murk...