Automatic Transmission Shifts without button press

I have an odd issue with a Duster I just bought and am restoring. The black button on the shifter doesn't appear to do anything. I can change gears from park all the way down to 1st without pressing it.

This in itself wouldn't be a problem except sometimes the shifter seems to move on its own from drive down into 2nd. And on more than one occasion I have accidentally put it in 2nd instead of drive because it's very difficult to figure out which gear I've selected without any real feedback from the shifter. In the past my previous Duster had a very solid "in gear" clunk type of feeling. If that makes any sense. This one feels sloppy without the button doing it's job.

Any advice?