I think dealing with museums really does need extra care as although everything might be done and agreed by all the parties involved at the onset, museum personnel can so often change and after a passage of time those earlier agreements can be overlooked or forgotten. I do not think for one moment that there is any dishonesty involved, it is perhaps just that the agreement is not known about and in mind at a later date by different new folks involved since the agreement was made..
I know of one incident of an owner offering to give wheels to a museum - they were fitted with good tyres when the gift was made and the gift was made on condition that the tyres would be taken off by the museum and returned to the donor. After a period of time, an enquiry was made to the museum about progress in returning the tyres and the simple answer was that they had to be cut off the wheels to get them off and thus ruined. The earlier agreement had been forgotten, overlooked or simply not known about by the different folks later involved. Cutting the tyres off was the quick and easy way out to get them off when it was just the wheels that were wanted. All a little disappointing when one tries to be helpful.