Prevent objects already in manual maintenance mode, entering automatic maintenance mode
If you, for instance, put several Windows Computers in maintenance via the scheduler and one of them was already put in maintenance manually, that one will get out of maintenance when the scheduler ends.
Same deal for hosted objects that were put in maintenance manually.
Also check here: https://social.technet.microsoft.com/Forums/systemcenter/en-US/e2af78b9-70b2-4282-b647-71f41dc0b476/scom-20162019-maintenance-schedules-stop-manually-configured-maintenance?forum=operationsmanagergeneral
This feature is planned for 2019 UR2. The furthest end time on the object will be honored with 2019 UR2.