This is resolved in NMS 7.5 with the new maintenance mode.
The trick is to enable the "Computer State Monitor" in NAS, and have it "Filter messages" for robots in maintenance mode.
When this is set, and you use the new UMP 7.5 USM functionality to put the robots into maintenance mode, then as long as the machine is rebooted prior to the end of the maintenance window, the alarm will be filtered appropriately, even after removing the robot from maintenance.
Setting the computer state monitor in the NAS forces the NAS to look at CM_COMPUTER_SYSTEM when alarms come in, and check if a machine is in "managed", "unmanaged" or "maintenance" state, and then act accordingly based on the settings you have set for that particular state. There should be no impact except that which is configured by the customer (i.e. alarms from 'maintenance' machines will be set invisible if they have that option selected...)