Commission Regulation (EEC) No 269/85 of 31 January 1985 amending Regulation (EEC) No 1760/83 on special detailed rules for the application of the system of advance-fixing certificates for certain agricultural products exported in the form of goods not covered by Annex II to the Treaty and derogating from Regulation (EEC) No 2730/79 with regard to payment of refunds on butter