Tweening filters becomes very slow

i am having a some movie clip buttons. each of these movieclips have a text in it. so on the rollover event of the movie clip, a filter will fade in gradually using the tween class. the tween class will change the filter’s alpha property on a temporary array and assign back to the movie clip’s filter property. when there is a rollout event, the glow filter fades away using the same method. it works but for some reason, it is very lag and slow.

the first time when i roll over and out the movie clip button, the glow filter fades in and out at normal rate. but as i move in and out a few more times, i notice that the tweening of the filter become very laggy. it slows down practically the entire swf movie.

i have had the text movieclips’ cacheAsBitmap set to true and i thought it should be better. i also had the quality of the filters set to low but they are all the same. i am using Flash 8.

i have no idea what’s wrong with this…