animation speed and the 'move to' action

I'm having an issue with the Animation Speed for my 'move to' actions.

I have 4 buttons on a page, and I have them expand and contract when each button is pressed (a flash-ish sort of animation). It works perfectly well when the animation speed is at the fastest, but if I drop it down one notch, I start getting strange things happen, such as buttons start disappearing and not moving to the correct locations.

Any ideas?