It's probably an issue with it making the rollOut and rollOver calls while the image is tweening, which changes the size of the "hit" area.

A few different workarounds to this depending on your particular situation.

You could put a shape under the image and make that the hotspot (instead of the image itself). put 2 keyframes in, make one the small size, one the large size and don't put a tween between them so it doesn't try to trigger the rollout or rollover during the tween.

You could also make a large background clip that tells the image clip to get smaller if it isn't already and remove the rollout command from the image.

Hope that helps!