The unanticipated acceleration of the December, 1984 AMPTE release transverse to the solar wind velocity is examined by a modified MHD fluid simulation. By taking into account the unmagnetized nature of the released ions, some of the essential features of the experiment are reproduced. These include a shift transverse to the solar wind as well as the subsequent downwind acceleration. The modified MHD equations, simulation results, and physical mechanisms are discussed. ¿ American Geophysical Union 1991