Chemistry sketcher update

Hello,

I am using a chemistry sketcher in a webpage and to update it I call a protocol on the  spsmChemSketcherUpdated event. It looks like this:

function spsmChemSketcherUpdated(ctab, base64encodedBinary, callbackData) {

      if(ctab!='')

            calculateMoleculeProperties(ctab);

}

After this kind of Ajax call I get a variable with my molecule information.

It works well except that the update is called not only when I update my sketcher but also when I scroll up and down (actually every time the sketcher becomes visible - or invisible).

Is there a way not to call the update in this case?

Thanks for your help!

Florent