Currently it's confusing when you click on the Parent Document Type lookup icon in the Document Type lookup. In that case, it takes you back into the Document Type lookup so you can lookup the parent. However, this is very confusing for the user because the page looks the same.
I'm not sure exactly what our options are here, probably one of:
1) See if there is some hook in the Lookup helper that would help us do this (still, in that case, not sure how you would determine the proper context so you would know when to display what?)
2) Create a whole new lookup definition for the parent document type (this might require another business object which may not be an option?)
3) Add support to the lookup framework for passing a request parameter that can override the default page label. Only issue with this is that we would need to have some way of telling the doc type lookup to pass this parameter. I'm not sure what the options are there.