Why are certain controls losing viewstate after UpdatePanel postback?

I've got several controls on a page .... then I've got an asp:updatepanel .... then I've got more controls after the updatepanel.

I call the update开发者_如何学GoPanel's Load event from javascript like this:

__doPostBack('<%=myUpdatePanel.ClientID%>','');

In the updatepanel's Load event, I can access all the controls above the updatepanel. However the controls below the updatepanel have lost their values.

What's the deal, Mr. UpdatePanel Man?