Check to see if your indicator control stalk is in the off position. Some cars I have driven, including Vauxhalls have parking light facility which uses the indicator switch. When the ignition is off and the key out, if the indicator stalk is in the left turn position, the left side side lights are on and vice versa for the right turn position. There is an audible warning when the door is open to remind the driver that one or other of the side lights are on. Try it and see.