Found a Bug with Boolean

 From:  TwinSnakes
Michael, here's a little more info.

As I continued to work and make my screw holes. I went to extrude them all at once, and that hole that was disappearing (before I closed and reopened the file) seems like it is "wound" wrong. All of them extruded in one direction except this one, it went in the opposite direction.

Maybe you can try it on your end. Well, I dont remember now exactly, which way I did it. But I believe it was just after making that last hole. Select the curves around the holes and extrude them.

You should see it then...hopefully.