rs, I believe that is the normal progression. Typical MOUs are binding, yet fall short of the fully detailed contract. They can provide a way for each party to be reassured that the other is serious about doing business and can allow certain compensated activities to proceed prior to a full-blown contract being signed... i.e. we'll pay you $XXX to develop a cost analysis and $YYY for a proposed schedule of delivery, etc.
Always tell the truth. Then you'll never have to remember what you said the last time.