FD-8 Effects sends question

[Top Jimmy]

Any one else have a FD-8? If so , why does the unit have what seems to be a mono effects send and a stereo(or left and Right) returns? When I hook up my effects unit and run back through my FD-8 I loose the stereo effect. What I'm saying is that when I turn up the effects return the tracks start blending together. If I have the effect return up I can no longer pan the idividual tracks.

Any help would be cool.