HI Rob
I have the Megrez 90 with genuine finder-scope bracket but I don't seem to have this problem. It connects with one screw as you mention but I don't recall having any problems with it. Seems to be secure and holds in place - not that I use it that often.
Perhaps an e-mail to William optics customer service may be able to assist. I have found them quite helpful and reply quickly to requests for assistance.
wo@williamoptics.com
Regards
Steve