paint Rect sometimes missing one border

[MarekR22]

Most of the time, the rectangle is painted correctly. But after resize, sometimes it will miss the red line boarder, for example the left-side edge is not painted.

Resize is the problem. When you resize graphics item and it has impact on boundingRect you have to call: QGraphicsItem::prepareGeometryChange (not inside boundingRect), see also QGraphicsItem::boundingRect.