Thieves lock a bike to yours, you return some time later and see yours locked to another so you swear and go away thinking the next day the idiot will have unlocked his bike from yours so you can get your bike back. Later that day/evening/night thieves return to open their crap lock and break your lock then steal your bike. You could try reporting, to police, that someone has locked their bike to yours and ask for assistance. They will laugh at you. If you’ve got proof of ownership, I'd suggest you get an angle grinder or something else to cut off their lock, after telling the police you will do that. Nobody will disturb you while you're cutting their lock off as bike thieves know that from their own work.
