Push the button....lock pops up....WHY?

[68 C-10 Panel]

Well like the title says, the passenger door wont stay locked. If I push down the lock knob and shut the door, it pops up as it closes. The driver door does that as well. However even if you lock it with the key, you can push the button on the door handle and the lock pops up. I have not taken the door apart yet, so I thought I would see if anyone here has ever had the same thing. Thanks in advance.