I have yet to work with the OE, so I don't know how it's implemented in eZP. However, I would think that the OE editor would substitute any XML datatype field in edit mode, or perhaps the is a specifc attribute that decides whether to include it or not.
You are using the XML datatype for your custom made classes, right? Perhaps you could tell me a little bit more about how the OE was implemented for the working content classes?
