Loading swf files into empty MC

My site has three frames, 1 is the preloader, 2 is the intro movie, and 3 is the main scene. In the main scene I have an empty MC called mainempty that covers most of the stage. The only part not covered is a small area at the top which has the nav buttons which never leave this location. In frame three of the main layer, I have an action statement which is
loadMovie (“A.swf”, mainempty);

The movie loads perfectly. Three of the nav buttons changes the pages by loading different swf. files into the empty movieclip. These nav buttons are located within a button that is within a movieclip. They are part of a drop down menu. When I selected one of the buttons, I added

on (release)
_root.loadmovie (“B.swf”, mainempty);

This loaded the movie but the entire stage shrunk to only the B swf. Then I tried adding an extra frame to the main stage, along with all artwork to extend it one frame (4). On the action frame of: loadMovie (“A.swf”, mainempty);
I deleted it. I just left it blank. The problem is still there. The movie loads but shrinks to just the swf file. How do I load a swf file and keep the main stage there?