QuickDesigner: Switching from transparent to solid does not repaint color picker

Steps to reproduce:

• create a Qt Quick UI / Application, have a component without an implicit set color (or you can use the border property of a Rectangle,...), switch to Design
• select the component, set the color (of the border) to transparent
• set the color back to solid

Current result:

• color picker does not get repainted - stays transparent
• the color gradient beside the color picker can be used to drag the Hue value - but color picker is still not repainted

Note: this is best reproducable with a Rectangle's border. Make sure to set the width of the border to sth greater to 1 to easily verify the change.