Easing movie clip problem.. PLEASE HELPPPP!

1

[FONT=Arial]Hey there everyone. I have a blank mc that has thumbnails nested in it, that scrolls up and down onPress of an ‘up’ button and a ‘down’ button. The thumbnails are 40x40 and there is a 5px space between them and they move up or down in 5 rows at a time. (I set the thumbnails to move (with an ease) 225 pixels up or down when you press the up or down button.)

The only problem I am having is when you click the up or down btns repeatedly. If the thumbnails have not finished easing into place when you click the up or down btns again, it will add another 225px to wherever it is currently at. This makes it so that sometimes only half or part of the thumbnail is inside the mask. I need to somehow disable the up or down btn after being pressed, until the thumbnails are finished moving into place, so that they move evenly on every press.
sorry if that sounds confusing. Any advice will help. Here is my code. THANKS

(i tried to solve it myself already using an if statement that is included down below in the code, but its not working)
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//easing function------------------------------------------
yPos = 0;
#include "lmc_tween.as"
function boxMove(yPos) {
    //yTo = where the mc is sliding to
    yTo = thumbnailCont_mc._y-yPos;
    thumbnailCont_mc.slideTo(null, yTo, .2, "easeInOutQuad");
}
//end of ease-------------------------------------------------------
     
//if thumbnails aren't done sliding into place disable up and down btns-------------
         //if y position of the container (thumbnailCont_mc) doesn't equal where its sliding  //too, set the up and down button to false
if (thumbnailCont_mc._y != yTo) {
    btnUp.enabled = false;
    btnDown.enabled = false;
}
//------------------------------------------------------------------     
//scroll thumbnails up     
btnUp.onPress = function() {
    //-225 gets put into yPos in the boxMove function
    boxMove(-225);
    trace(yTo);
};
//scrollthumbnails down
btnDown.onPress = function() {
    boxMove(225);
    trace(yTo);
};