Happens alot with the older 206A/B with the single latch doors when they have been retrofitted with wedge windows. Leave the rear windows open a little tends to stop it.
Also on the 355/350 with the short door when rear sliding doors fitted. Normally caused by the plastic latch being worn or broken.
As nick says catch your map put the coffee down slow down and kick it out of balance to close the door. Avoid leaning over to shut the door a few a/c have been written off with knees knocking the cyclic.
