Sorry, I don't know what SP-1 is, nor do I really understand the answer you have given. When you say 'it was calculating work remaining', where was that shown? Was what I thought was a total of time taken (in the actual work column) in fact a total of time left to use?

To stop this happening again should I avoid using the %age complete button? Or was I barking up the wrong tree trying to use Project to assess the accuracy of our time estimates?