Re-center Modal Popup with Javascript

Question

I have a modal popup that initially shows some content but expands a div if a checkbox is selected. The modal expands correctly but doesn\'t recenter unless you scroll up or

Answer 1

Here is what it is:

$find('ModalPopupExtenderClientID')._layout();

For example:

$find('detailsPopUpExtenderId')._layout();

and in aspx:

BehaviorID being the property where to set the clientside id.