On mac drag'n drop to trash in dock has no effect

Start QtCreator, switch to viewing the "file system" at the top left. Attempt to drag and drop a file to the Trash on the dock has no effect. Dragging and dropping onto a folder in the dock does work. The same happens on application where is a simple list showing files. The drag is setup like this

QList<QUrl> list; 
for( const QString & url: urls ) { 
    list << url; 
} 

QMimeData* mime = new QMimeData; 
mime->setUrls( list ); 

QDrag *drag = new QDrag( this ); 
drag->setMimeData( mime ); 
drag->exec( Qt::CopyAction, Qt::CopyAction );