Script doesn't hold up over timeline

Let’s say I have a timline that is 50 frames. At about every ten frames there is new MC with the following script.


Really simple. they just fade in over eachother. But when I tell the last frame to gotoAndPlay(1) the alpha fades seem to increase thier “speed”, until about the 5th time the timline has looped through there is no more fade, the image just pops into place?
Any idea why, or is this bad code?
thanks for any help