modal UI dialog is recreated every time?

modal UI dialog is recreated every time?

I've noticed that if I created a modal jquery UI dialog with an iframe inside, the iframe gets reloaded every time the dialog is opened.

This doesn't happen if the dialog is non-modal. I've verified this on Firefox 3.6.8 and Chrome 5, does not happen under IE 8.

Is this normal behaviour? Why would a modal dialog be recreated each time it is opened?