LGPL w/r/t plugins - are they derivative?

Hi, xwikiites. I was wondering how you regard plugins that extend the capabilities of xwiki with resepct to LGPL license. Do you consider plugins to be derivative works? (I am assuming that they are not already derivative in tthe sense of being constructed on top of an existing LGPLed code base) For instance (purely hypothetical): Commercial developer "D" develops a type-ahead plugin that fills in names of people in his office. The system is so successful, that he plans to market "TAXWiki" - based on the xwiki codebase, but with the added feature of corporate-aware type-ahead. Would the LGPL require that D contribute the source code to his type-ahead plugin back to the xwiki codebase? Thanks very much, -apperson