Can you disconnect the phone to see if the Sills work correctly?

As you say, only other item to stay on for a few seconds, when the engine is turned off, is the radio. The heated seat timer is set for 5 mins. Doesn't sound like a loose wire. Does it matter how far you open your door? Does it happen with both driver and passenger doors? Does the sill light up if you open the boot or if you turn the interior lights on?

You could contact the guy who did your phone :idea: