I replaced the power door lock solenoid on my drivers side on my 86 just about 2 years ago. Well, just recently, it stopped working again, but with a slightly different variable... Now when I lock it by pushing the peg down on the door, and then shut the door, it unlocks again. But if I push the peg down and shut the door while holding the handle open on the outside, it will stay locked when the door shuts. And then when I put my key in to unlock it, and turn it, it pops up like it when I hit the button... Hopefully this makes sense, but I'm curious if this is just me needing to replace the solenoid again, or if it is something else that is causing the problem. It's seems weird... idea's?
Your lever on the door catch assembly is bent going from the door peg to the door catch.
or
The rod from the door handle assmebly to the door catch assembly is bent.
to check,,,,,,,,,,,
remove door panel
observe the two rods both the door peg and the door handle rod.
move them and watch what happens by moving things on the outside.
now..
reach in and move the door peg all the way down and the door handle rod up and down.
you will see a difference in distance.
the door catch or door latch assembly lever is like a mouse trap. If the lock or unlock / open levers are not fully enguaged, it wont take much to make the spring in there undo what you just did.
I will bet you can bang the door and make it unlock as well or just by simply locking the door and slam it shut.
your problem is mechanical.
it's not the impact of the door shutting that is unlocking it, it's the door latch locking in that is causing the lock to unlock. my buddy had an old mazda that did the same thing because that's how the company built it. He had to hold the door handles on both front doors when he shut it, or else they would unlock. Mine is doing the same thing as that, but started sporadically...