Dear Jeffrey,
thanks for your interest.

Here's the code for one of the extenders that shows the problem:

[ProvideProperty("BrowseButton", typeof(Control))]
public class FolderBrowserExtenderProvider : Component, IExtenderProvider
{
 private Hashtable extendees;
 protected FolderBrowserDialog folderDialog;

 public FolderBrowserExtenderProvider()
 {
   extendees = new Hashtable();
   folderDialog = new FolderBrowserDialog();
 }

 [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
 public System.Windows.Forms.FolderBrowserDialog FolderBrowserDialog
 {
   get {  return folderDialog; }
 }
       
 public bool CanExtend(object extendee)
 {
   return (extendee is Control);
 }

 [DefaultValue(null)]
 public Control GetBrowseButton(Control extendee)
 {
   if (extendees.Contains(extendee))
       return (Control)extendees[extendee];
   else
     return null;
 }

 public void SetBrowseButton(Control extendee, Control browseButton)
 {
   if (extendees.Contains(extendee))
   {
     Control btn = extendees[extendee] as Control;
     btn.Click -= new EventHandler(browseButton_Click);
     extendees.Remove(extendee);
   }
   if (browseButton == null)
     return;

   extendees[extendee] = browseButton;
   browseButton.Click += new EventHandler(browseButton_Click);
 }

 // browseButton_Click omitted for shortness
}
-------------------------
Hope you can reproduce the behaviour.
It only occurrs when you try to assign a control to be its own BrowseButton
via the VS designer.

Regards,
Martin Müller