This should be an easy fix for GS I hope? Are you able to specify the normal direction (the visible side of the glass pane) when using the PLANE command Barry?
While that works, I wouldn't call it a good solution. You can no longer edit the casework object short of deleting it and creating a new one. But in the interest of getting some rendering work done in the meantime, it'll do. Thanks!
In a recent model I went and created slim glass walls for all my cabinet doors. It was time-consuming but it worked.