qproperty-icon in QToolBarExtension does not work always

See attached .ui file including the stylesheet in it.

I have multiple toolbars within a ui file. Each Toolbar contains some toolbuttons, when these doesn't fit into the toolbar, an arrow is shown. this arrow can be overwritten by stylesheet.

The background-color property works always.
The icon property doesn't work always (see screenshots)
So sometimes when dragging in and out, the icon is shown sometimes not

stylesheet:

QToolBarExtension {
 background-color: blue;
 qproperty-icon: url(:/arrowRight.svg);
 }

Additionally, it would be satisfying to set another icon for the vertical toolbar arrow.