Yeah I know it was supposedly turned off, but it could still be SWAS kicking in. There is a bunch of threads on MSF where people had the same/similar issues where the car goes extremely rich and hesitates under partial or full throttle, even in a straight line or when strapped to a dyno, and it was SWAS.
If you really want you can just unplug it, or get a switch wired in. How to: Install a switch for SWAS enable/disable - Mazdaspeed Forums