Byerly Boa System Bindings Problem

My problem is after my first hard landing, the Byerly "BOA System" bindings open up for no apparent reason. These binding have a heel-side wire cable. I have tried everything on land to duplicate the problem but to no avail. These are out of warranty but still relatively new bindings that are giving me fits. Any suggestion on what is causing the bindings to open up after a hard landing? Upon tightening them while riding after they initially open, the problem for the most part fades away. Is there any repair or adjustment to be made to alleviate this problem? Thanks.