There's a clue in the second sentence of my initial post that may answer your "concerns"; I also believe the date of the referendum has yet to be announced. Capiche?
All Schulz is saying is that to be legally binding any agreement by the Council and the UK also has to be approved by the European Parliament; that's not a surprise surely and isn't it desirable?
Why would the UK government decide to hold a referendum before this has been done?