The technical explanations offered are the most likely, but also
remember that if you inserted a lot of coinage you may have exceeded the
limit on legal tender (eg a vendor is not obliged to accept 70 10p coins
in receipt for a 7 pound item).

Drifting off topic here...

It is true that a vendor would not have to accept the coinage but it isn't
anything to do with legal tender. He doesn't have to accept 7 one pound
coins to pay for a 7 pound item if he doesn't want to even though it is
legal tender in the UK.

Legal tender is a means of payment that should not be refused by a creditor
to settle a debt. If you are buying a ticket, or paying for an item in a
shop there is normally no debt involved. On the other hand if, for example,
you are eating in a restaurant where you are billed at the end of your meal
then a debt is involved and legal tender should be accepted in settlement.