Well, what time does your MXwindow last? If it is just 2 hours and 1 minute, it may pick up delay if there is no other MX window which can bring the aircraft to reasonable condition. You should leave about +3 minutes in your MX window to account for any delayed flights, else you might keep getting delayed from maintenance messages. The MX must happen (there was a suggestion to keep departure time in spite of not yet completed maintenance, but it was decided against it, and MX will be kept to bring aircraft to the same condiition as MX would do during on-time arrival).
From the sceenshot, I think the issue is, there's a single daily 7h50 maintenance window, giving a 132% maintenance ratio. Since at some point there was a 1 minute delay, the maintenance is stretched as well, finishing 1 minute later to keep the same 7h50 window, even though a 7h49 maintenance window would be quite enough to return the aircraft to 100% and the extra minute is unnecesary.
Stretching the maintenance makes sense when you have tight maintenance schedules (for instance, if delay causes a maintenance window of 1h59, it makes sense to use an extra minute to ensure maintenance will be done). It doesn't make sense, however, when maintenance time is scheduled in excess as is the case here.
Of course, I'm not sure how easy or hard it would be for the code to account for these different scenarios. Maybe only a one-size-fits-all coding is possible.