Glyph shapes are defined with a clockwise path direction meaning the area
inside the path should be filled.

RoundRectangle2D is used for strikethrough on text and this path is
defined in an anti(counter)-clockwise direction.

If text is painted as a filled shape rather than using glyphs images - as
happens for many effects and very large text, the strikethrough the opposite directions
mean the interesection has a winding number of zero and is outside the path so is not filled.