As above – as standard pressing the Mini logo unlocks all doors and the round button above the logo locks them BUT I do seem to remember some way for a dealership to ‘reprogram’ the key to lock/unlock in a slightly different way.
However it is also possible that the passenger side door lock is just being a bit sticky – ours occasionally does that (53 plate we’ve owned from new). Try cycling the open/close via the switch or opening and shutting the door a few times via inside handle. You can also tell if locks are playing up by listening for ‘clunk’ from door when you set off (doors automatically lock at 5-10mph).
Great little car – I agree it’s not a ‘proper’ mini though – our Cooper S starts first time, is quicker than a ‘classic’ mini, the supercharger whine is lovely and it handles better… You can keep old mini’s (unless it is Project Binky :))