I have a flickering rollover problem

Hello,

I have made a simple rollover using two vector images, including a lo-light and a hi-light state.

The problem is when you mouse over the rollover it tends to flicker or revert back to the lo-light state while the mouse is still hovering over it.

If i use rasterized images this problem seems to go away.

Does anyone know why this is the case ?

I’ve included a zip file containing the relevant files and a demo .fla and .swf displaying the issue.
Any help greatly appreciated.