Problem with buttons

I’ve got a set of buttons in a flash movie. In their Up state they have a bitmap background and a label in one font. In the Over and Down states they have a different movie clip background (containing a shape) and a different font, so that obviously when you hover over them they change.

My problem is that although the movie as a whole doesn’t take that long to load, when you first hover over the buttons, nothing happens for several seconds. The mouse pointer doesn’t even change to a hand to indicate it’s a button for several seconds. It’s as if the Over state were taking time to load when it’s activated.

Is this simply because the buttons are too complex/large? And is there a way to force the movie to load the Over states when it’s loading everything else, rather than when you first hover over them?

Hope this makes some kind of sense! Any help appreciated.