upload profile picture flickering

When I upload a new profile foto I can resize the picture or select only a part of it. This is done by a blue line with some knots on the edges/corners. Within my site this blue line flickers. It is there and one second later it is gone.
I’m speaking of the class “cropper-dragger” in the source of the page

The page I need help with: [log in to see the link]