Lock Mercedes Benz using inside lock while door is open

I have a 2012 Mercedes Benz GLK 350. With
my previous vehicles, I’ve always been able
to throw my keys in my purse and still be
able to lock my car when I exit it by hitting
the interior lock before closing the door.
When I try it now on the Mercedes, though, it
locks every door except the drivers door,
since that’s the door that is open. (On the
passenger side, I can’t lock the doors at all
when that door is open). Is there a way to fix
this? It would be much more convenient for
me to get my keys put in a safe spot before
grabbing my purse, diaper bag, and infant
son?