We are aware of a similar to the the described issue and it has been logged into our bug-tracking portal. You can track its progress and vote for it here: A large uploaded image is not saved properly after cropping in disabled CanvasMode
I will contact our developers in order to increase the priority of the bug. Unfortunately, the only workaround I could suggest you for the moment is to use the ImageEditor in enabled CanvasMode, calling the control's saveImageOnServer()
method in the ClientClick handler of the button.
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