Hey Twinblake,
i am trying to achive the same, but i am stuck as you are...
[attachment=0:18sq3bug][/attachment:18sq3bug]
it seems like the *dt not work within functions. if i leave the function away and just do the script so it fades in and out again smoothly as it should. but as soon as i put the action within the function it stops to work, even if i call the function. however wenn i set a total value of opacity in the function it also works...
to be hornest i have no idea whats going on there O_o