Bought my M&P 22c less than a month ago and finally got it out to shoot yesterday for the first time.

The rear sight seems to have a spring action that pushes the sight up until it meets the screw that adjusts elevation.

I let a guy shoot it yesterday and he started messing with the sight and said that when he was shooting it, the screw was coming loose and was peering into his sight picture (unlikely but that's what he said).

Now the spring action isn't working, and the sight freely moves up and down.

What are my options? Is this a common problem?