We had a King Air do the same thing at my airport once.
I was sitting at the end of the runway waiting for release. Gray Clnc Dlvry said they had a King Air inbound on the ILS to our airport(Untowered). He never made any calls on the CTAF but we saw him land, taxi off, and park. ATC would not release us because the King Air had not cancelled. I told them I could see the King Air in parking, engines off, and people getting out. Still would not release until they called. Because the fuelers were out at the King Air, noone answered the phone when Gray called. We ended up taxiing back to parking, instructor got out and told the pilot's to cancel their IFR so we could leave. I wanted to tell them they were number one, and hand them a bill for some hobbs time in an Arrow, but I did not.
Is it normal not to be released because of this? I can understand waiting for an approach, but if I am telling ya I saw it land, are they just being difficult?