Don't forget that Jet2 (Channel Express as was) have maintained a base at Stansted where the aircraft (a 737) is used specifically for passenger charter work of all kinds. Can't say for sure but this could be the aircraft involved in the series of BHX flights.
Also fair to say that the schedule from the main bases is still not in full operation - from Leeds some of the current daily routes still have to go double / tripple daily whilst other destinations (Toulouse, Almeria & Valencia) don't start until next week.
I would counter MUFC fan's asertion that bases without competition are less important - I reckon Jet2 are able to extract better yield from these bases than those where they are subject to ZB, EZY and the suchlike.