We are experiencing a serious problem with custom server controls in the web
designer of VS2008. When we perform an action within the designer that causes
the markup to be updated, there are many   characters and spaces inserted in
between the tags of the server control. For ...

I am building a Webcontrol.
public class MyCustomControl : WebControl, IPostBackEventHandler,
IPostBackDataHandler {
 .......

Can anyone please suggest things can cause a dropdown box to stop causing a
postback?  (besides unchecking the 'enable postback' box)
One of the last things I was doing was creating modalpopup extender panels
which which use update panels that refer to the dropdown box... but I ...

I have created a series of Composite Controls, inheriting from
CompositeControl, which of course implements INamingContainer. Below
is a snippet of simplified code to show how I'm using these controls
in the page.