Problems to add a custom web control

[Erik Cruz]

Hi.

I have a library with four controls. For each one I set the toolbox
attribute like that:
<ToolboxData("<{0}:controlname runat='server'></{0}:controlname>")>

All of them works as expected except for the class that inherits from an
imagebutton. For that, if I define the toolbox attribute, when I drag the
control to a form the html is written this way:
<cc1opimage runat='server'></cc1opimage></cc1opimage>

Notice that the html includes the closing tag twice, but this behaviour does
not occurs for the other controls that inherits from linkbutton, hyperlink
and button. What am I doing wrong?

TIA,
Erik Cruz