"Richard J." wrote in message ...
But that's the coin box that holds all the coins from completed
transactions. There must also be a smaller box that temporarily holds
the coins from one transaction so that they can be returned if, for
example, the user cancels the transaction before completion. I guess
your attempt to feed £7+ of small change filled up this smaller box.

I suddenly realised that's probably what it was, not long after I posted
the question (isn't that always the way?).

Out of interest, does it do the same thing with notes? Or if you cancel
after putting a note in, do you get the equivalent back in random small
change? If so, it must get the change from somewhere...