Control Masked MovieClip


I have a movieclip with a few frames and stop actions on each frame. This movieclip is being masked. What I want to do is be able to change the frame of that movieclip while the mask animation is running (mask expands to reveal content below). However, when I try to use a gotoAndStop(2); command to the movieclip during the masking animation, the frame that movieclip is on does not change… Is there any way I can control the frame that movieclip is on during the masking animation?