velocity of massless particles and velocity of flow field in same coordinate
 

I am using massless particles(Only available in ANSYS-FLUENT v.12)in discrete phase model to trace the flow field in a complex geometry,when I check the velocity of particles they are not equal whith velocity of flow field in the coordination of particle,But is seems resonable that the velocity of massless particles and velocity of flow field in same coordinate should be equal,I am totally confused,what is the reason for this Discrepancy?
Any Ideas welcome.:)