Hallo Marco,
One of two ideas:
(1) Remove the onCellClick. This is the guy that is sending the request to the server. And add the click onto the image.
(2) Add this following string onto the onClientClick "event.cancelBubble=true;" to prevent the event from been handled by someone else. Probably you only want to do it if htmlbevent.cancelSubmit is true.
Recommended would be (1).
++bcm
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