Updating the value of a Q_PROPERTY-ENUM using a stylesheet

class Gallery : public ScrollArea 
{     
   Q_OBJECT     
   Q_PROPERTY(Alignment alignment MEMBER alignment) 
public:     
   enum class Alignment { top, left, center };     
   Q_ENUM(Alignment)     
   Alignment alignment = Alignment::center;
};

Gallery
{ 
   qproperty-alignment: abc;   /* any value !=  than left or "left" is ignored, alignment remains left */   
   qproperty-alignment: left;   /* alignment becomes 19, why? (?)*/   
   qproperty-alignment: "left";  /* Inside quotes, as: "left", "right", both works correctly */
}