Here is a sample that has a sub-classes browse dialog.  It was created just as my explanation above mentioned.  So if you are getting errors on this sample, then you do not have the most recent version loaded or still have old assemblies that are being referenced.

OK Trent,

now I understand my errors:
the 3 properties BusinessObjectType, SearchFields, BrowseResultsLayout must be set from within the class itself, and not from the form in design mode.

all attempts to reset these properties in form design mode are without any result, only class-set properties are saved.

If it's "by design", let me use it as it is...

Yup, that is by design.

Thanks again for all your advice