GraphicsItem jumps back to original position

[Ozzi]

Hi Qt Fans,
I have just started to learn about QT. I made a small app which adds rectangles to the screen and allows them to move about when dragged with the mouse.

Facing a small problem though. Every time the rectangles are moved, they keep jumping back to their original position at startup.

Anyone know what could the problem be?

My project can be downloaded here.
Google drive link

Thanks .