[Koha] Opac XSLT: Problem with displaying of authorized values

I want to define authorised values for some fields - for ex. 657 (Term of function) or 650 (Topical term). However, in OPAC (with XSLT on), the content of these fields doesn't appear, but there appears only the letter "a". I removed the definition that the fields 657 and 650 contain authorised values, and everything was OK, so the problem must be in how Koha display fields with authorized values. Would anyone know how to fix this problem? Thank you Ondrej Mlecka Casa Balthasar Roma