Trouble with simple 2 image fade with links

I’m trying to do a simple two image fade where if you click on the image it will take you to a URL (different for each image). It seems that I cannot have a button that fades in/out so I have two layers, one the image the other the button. However, when it animates it appears the button is slightly scaled differently so when the fade happens there is slight contraction of the image. I’ve doubled checked the scale of the position of the images and buttons are all the same. How can I accomplish the simple effect?

Put the button inside a movie clip. You can do anything you want to the movie clip.

Thanks! I was like "movie clip?". Then I click on the "Advanced" tab... "Ah ha!"