12181 Driving on the toll roads

I've been meaning to mention for months now something strange that happened to me last autumn.
So I get on the A1 at Chiusi and get off just up the road at ValdiChiana. (It's far easier and sometimes just as quick to take the back roads but I was on auto-pilot and off I went.) Pull up to the toll booth at Val di C with my Euros 1.40 ready to pay. I was in the automatic machine line, not the queue to pay the man. Popped my ticket in the slot, was about to drop in my 1.40 cash in to the bucket when the sign illuminated, "ticket invalid". So I pressed the button and very promptly a man answered, I told him what the machine said.
"You are on the A1, signora."
Er, yes.
"Your ticket is not valid for this road."
Come?
I explained I had got on only one junction down at Chiusi.
"Then you have been on the road too long. Your ticket has expired."
Eh? I only got on 15 minutes ago, I didn't even stop for gas or a coffee at the local eyesore autostrada caff that straddles the road at Montepulciano Est.
I began screaming and shouting and in order to shut me up he simply let me through.
But it started me thinking: is there a limit to the amount of time you are permitted to spend on an autostrada? And how on earth could a driver be in possession of a ticket for another toll road?
E strano, eh?