Had the same problem with my buttons, which are basically the same as yours except I use an effect, but I fixed it like this:
Cursor is over "Button"
----> Pick all "Buttons" : Disable Effect
----> Pick "Button" nearest to Mouse.AbsoluteX, Mouse.AbsoluteY : Enable Effect
Cursor is NOT over "Button" : Disable Effect
So what it does is, as you move the cursor over a button you start by removing all effects from any buttons, and then you apply the effect to the button nearest to the cursor.