I live in Barcelona / Spain and recently got fined in a Metro for something I had no idea was illegal.
I entered the Metro zone with my girlefriend and we both used the same card (It's legal with that card - T-10). Therefore I had two timestamps left on the card one after another.
My girlfriend left the metro one station before me, and as she was walking towards the exit she got stopped by the control. She didn't have the ticket as the ticket was with me, and she got fined.
Overall: The rule that you have to exit the area together is nowhere to be found in the Metro area, how ever it can be found on their website.
On the metro, you should stay together for the whole journey , from the entry point station until leaving the metro premises.
I wouldn't mind paying the ticket if the rule was clearly visible either on a ticket, or in a metro area - which is not a case.
I went to their office to complain and when I asked them where is that rule, they replied: "Well... It's logical..."
Are there valid defenses to this rule that could be used?