Not sure if this fix ever made it in (I assume it did), but I’ve got a similar issue popping up (not sure if it’s worth a new topic).
On 3.15.1:
1/ create control, set 2-4 control maintenances by date, correct number of maintenances are created (i.e. 3 for a semiannual on 5/31 and 11/30, created today for a total of 3)
2/ edit the control, for example, changing service owner or maintenance owner
3/ An additional maintenance is created when the record is saved → in this case, a second 5/30/2023