First Drag for drag&drop does not work properly.

First Drag does not work properly :

• drag icon is not displayed
• drag and drop is very slow or does not work at all

I have seen the problems with the QT examples :

• puzzle http://doc.qt.io/qt-5/qtwidgets-itemviews-puzzle-example.html
• dragable icons https://doc.qt.io/qt-5/qtwidgets-draganddrop-draggableicons-example.html

After the first drag & drop : everything works fine.