Modal doesn't show if child control is not visible

Hi,

I've made a modal using ModalPopupExtender. The modal works normally until I set a asp:panel to visible = false (for c#) or display:null (for css) which causes the whole modal not to display at all.

So basically, it looks like

<parentPanel>
 some other stuff<childPanel Visible="False">
    more stuff</childPanel></parentPanel>

The childPanel is only shown if the user meets a certain criteria which is checked for at codebehind