about ModalPopupExtender and panel

Hi:

I use ModalPopupExtender to make the popup screen, and the screen built by panel with severval textbox on it.

The problem is, once I perform ModalPopupExtender1.Show(); The data I set to the textbox will be disapper,

I means I denominate some values to the textbox which on the panel, and when the ModalPopupExtender1 shows, 

the content of the textbox will be empty, not the value I set.  In addition, the button which I click is put on the UpdatePanel;

If not, it can work, but if the button is on the updatepanel, the textbox will be empty.

If there any solution for that, thanks a lot.