The linguistic annotation of natural language corpora is one of the main areas of computational linguistics. Much energy has been devoted to building large syntactically annotated corpora, which are also called treebanks after the phrase-structure trees they contain. For some time now, functional information, i.e. information on whether a constituent functions as e. g. subject, object or adverbial, has also been included in the annotation. Yet, while at first glance this may not seem to be a venture too complicated, matters are not always as easy as they seem.