glutPositionWindow

I’m working on yet another GUI toolkit based on GLUT and I’m trying to build subWindows that can be repositioned interactively but I am having a weird behavior from the MotionFunc callback wich re-enters multiple times with different values also if the mouse is not moving, creating a ghosting effect.
I have the feeling that when I issue the glutPositionWindow command, by the time I re-enter in the MotionFunc the GLUT subsystem hasn’t recorded the new window position yet. As of now I am stuck.

Did anyone have a similar experience? Any known workarounds? Am I hitting a GLUT limitation?

Thanks.