Overview window box updates inconsistently with hidden rows/columns

Set up an alignment with hidden columns at the far RHS. Size the viewport so that the overview window's red box can move off or on to the hidden columns. Click and drag the mouse up and down along the left edge of the hidden column region in the overview window. The red box flickers between having its rightmost edge at the left of the hidden column region, and at the right of the hidden column region.