arckal: As long as you're in "Remove" sensor mode on the A+ and you put the sensor/lock in inclusion/exclusion mode, they will unpair. You can remove a sensor even if the A+ doesn't list it, it just reports "Unknown sensor removed". I've gone through the "Remove" process several times even if it's not listed on the A+ to ensure the lock has been excluded.
Again:
On the A+
From home screen, go to the "Add Sensor" option, then select "Remove"
On the Schlage:
Lock the deadbolt
press the schlage button
enter the programming code
press 0
If you get the green check, it's successfully removed. If you get the red X, the lock still considers itself paired.