Reference planes have directionality in that one side is considered the front or positive build surface. The way we draw a reference plane dictates that direction. Drawing the extents of a reference plane from top to bottom in plan results in a different plane than if it were drawn from bottom to top. For the plane drawn top to bottom, the positive direction for an extrusion built on that plane will extend to the right. For a reference plane drawn from bottom to to, the positive direction for the extrusion will extend to the left. This has huge implications when building families. It would help if we had flip controls to fix the erroneously created reference planes.
