ListBox outline

The header component used in a ListBox appears to bugger up the outline. It gets drawn on top of the outline for some reason.

My header component has a filled background, so the paint function has a

g.fillRect( 0, 0, getWidth(), getHeight() );

however, if i have an outline (of thickness 1) on my ListBox derived component, the bit of outline at the right-hand edge of the header is overpainted by the header unless i change the width of the filled rectangle to getWidth()-2.

is this a bug, or is there something wrong with my brain?