Door lock (lock portion only, unlock works fine) button functioning oddly

the door lock button (lock portion) is just plain funky. What it does is when the key is in the ignition and you turn it. Not necessarily on, but turn it just to the point of firing the spark to start it, then the lock portion of the lock button does not work. Same if the car is on and running. But, when the car is off and in park, I can get it to work. And it's only the lock. It unlocks just fine no matter what. And the button to lock and unlock on the passenger door works perfectly. Small and some what insignificant thing but wondering if you have suggestions on that now. :)

Thank you