Just experienced the same situation, stopped at petrol station and needed to get my wallet out of the locked boot. My I drive setting is 'lock when driveaway', so I pressed the door / boot unlock button and at the same time opened the drivers door, the locks made a double clunk and I exited the car, went to the boot...locked so went back to get into car and all doors were locked, keys in ignition & engine running as a side the door lock indicator on the drivers side was only halfway down.

Mobile phone & BMW assist phone number were locked in car so had to leave the car running for 15 minutes whilst I used a nearby restaurants phone to get numbers.

BMW assist arrived 1hr later and used two small air bags to move the top of the door away from the car then used a long pole to press the door release button, simple & effective!

He reckoned that he had only seen this happen once before

?. lessons to be learnt:
1) don't multitask by trying to open the door & press the release at the same time
2) take keys with you!

 

For some additional information about the door locking issue, read question #2 from the following thread:
http://forums.e60.net/index.php?showtopic=12375

 

Suggestion: Hide the plastic somewhere outside the car. Use some duct tape to stick it somewhere.