Was the lock broken?

Inside the door, the locking mechanism to the interior lock is either bent or disconnected. Just remove the door panel to see this.

I had a dart the same year and no that is not normal, as stated above the door panel has to come off to find the damaged component.

Most likely the rod that goes from the lock button to the latch has fallen off. When you get the door panel off look for it in the bottom of the door or dangling from the latch inside of the door. There should be a little clip to hold it in place. Hope that helps! Jim