swapthDepths and player versions

I have 4 mcs across my stage (slightly overlaping eachother) and I’m using the following swapDepths script on each of the different mc rollovers…

instancename_mc.onRollOver = function () {

When I publish with fp6 (AS 2.0) is works great but with fp7 (AS 2.0) the swap depths sometimes acts weird. When moving the mouse across the different mcs it occasionally brings the new mc to the top (like it should) and puts the previous one back to the bottom (when the previous one should stay directly below the new one). Any ideas as to why this happens or how to fix it?