It is still happen in the sample. 

 

The problem doesn't occur with the code 

   Dim Image1 As New System.Web.UI.WebControls.Image()
   Image1.ToolTip    = "Insert today's date"
   Image1.ImageUrl    = "tools.gif"
   Image1.CssClass    = "CuteEditorButton"
   SetMouseEvents(Image1)
   Image1.Attributes("onclick")="Testing();"
   tc.Control.Controls.Add(Image1)

 

But it will be a problem with this

   Dim ctrlTwoColumns As System.Web.UI.WebControls.WebControl
   ctrlTwoColumns = Editor1.CreateCommandButton("Testing", "download.gif", "Testing")
   ctrlTwoColumns.Attributes("onclick") = "Testing();"
   tc.Control.Controls.Add(ctrlTwoColumns)

 

Maybe something wrong with System.Web.UI.WebControls.WebControl when receiving doubleclik event