Actionscript Code:
window.startDrag(false, contenedor._width)
and it seems to do the job, you drag the window and it only slides on x coordinates, not y. But the window movieclip get out from it's original position! I checked the contenedor movieclip registration point, is left centered, I tried changing the registration point right, up center, down center, down left, down right, up right, up left, etc...and also on the window movieclip, lol. The window is in its position, but as soon as I press it to drag it, it moves like half the pixels up.