Hi,

if it is wired to two controls, it will run twice, no question about that -
this has nothing to do with SQL Server's subqueries :-). Controls do not
know about each other unless it is explicitly somehow stated by the page
developer. Controls cannot assume much about logic - like the logic run on
their Prerender event , as the assumption could be wrong, too.

Instead of hardcoding the controls in the event handler, you could rely on
event being raised for specific control and deal with only it.

You could for example run it like this:

//Wiring events somewhere
tbPswd1.PreRender += new EventHandler(tbPasswordPreRender);
tbPswd2.PreRender += new EventHandler(tbPasswordPreRender);

 protected void tbPasswordPreRender(object sender, EventArgs e)
   {
       //Use the knowledge that control raising the event is available via
sender argument
       TextBox tb=(TextBox)sender;
       tb.Attributes["value"] = tb.Text;
   }

When it works equally for all TextBoxes you assign this handler to.