Alpha Leader
I understand your point but the sequence for hand over is that first there is a co-ordination between the two ATC units in which the handing over control unit offers the traffic to the receiving unit under certain conditions the main one of which is the flight level of the aircraft concerned. If this is accepted by the receiving controller the hand over takes place. If it is not acceptable due to other traffic already in the receiving controller's airspace he would refuse the offered co-ordinartion and request a different level or a delay perhaps rarely with one or two orbits at the same level to ensure separation and to resolve the confliction. This should all take place BEFORE handover and not afterwards.
Suplementary questions would be: was the aircraft at the c0-0rdinated level? or was there a correct co-ordination with a level bust?
Only time will tell but these are questions that must be asked