Improving performance with overlapping MCs?

Question

I'm having some performance issues in certain areas of a flash game Im making.
Here's the situation:
I have big movieclip containing a map that can be scrolled and scaled. There are some pannels with a bunch of MC buttons, controls, etc. on the right side of the stage. These are seperate from the map and stay in the same place.
Everything runs fine untill the large map is  zoomed in and/or scrolled such that the right side buttons and stuff are overlapping them map. Then the framerate jumps down from a nice smooth 30 fps to about 3 fps while the map is moving. There are no issues with the map moving when they don't overlap.
Now the thing is, is that's there's no real interaction between the buttons and the map. No transparency or anything, in fact I'm perfectly happy with the map dissapearing behind a side pannel. There are only about 3 pannels that the screen drawing routine would have to worry about, as all the buttons rest on top of the pannels, so why is my performance taking such a hit?
(Hmmm. Actually I do have a lot of transparency, but each is on top of a solid background, and none interact with the map.)

Answer 1

I did do some reading on it. I tend not to use code without understanding how it works - at least a rudimentary understanding.
At the moment, I'm not changing anything about how the buttons look - size, rotation, placement, color, etc. This suggests that I can keep them cached starting at runtime while testing the cacheing. (Though I also tried caching them when starting the simulation, and disableing cacheing when the buttons could be used, too.)
Basicaly, I have a game where you use the buttons to supply program commands to robots on the map. Once this is done, you run the program, and the robots execute their programing. Meaning that you can't issue new commands while they are running (and the map is moving), so the buttons are disabled. So there is no reason they would need to change in appearance. When in the 'programing' stage, the map is not moving because the sim is not running. This seems to suggest that cacheAsBitmap could be enabled at all times.
At the moment, I've had to resort to making the _visible property of the button pannel = false during the sim stage. However, this is not an ideal solution, it's just what I've had to resort to to be able to test the workings of the game. eventually, I'll want the player to be able to see how the commands are executing while the sim is running.