Error with jump function when putting script on movieclip - actionscript-3

Question

I'm having a problem with my jump function for a platformer engine. I've moved all of the hit testing onto the individual platforms in the level, so I don't have to write things out for each individual one. The problem with this is that only the first movieclip added to the stage can be jumped on to. The others just make the player sink through the floor if up is held down (as they should- as he's not meant to be there there's nothing to stop him).
So the problem is that the check for the jump just isn't registering properly on the second block. Here's the code (sorry about the excessive MovieClip(parent) s)
var playerRef:MovieClip = MovieClip(parent).player;
stage.addEventListener(Event.ENTER_FRAME, hitUpdate);
function hitUpdate(e:Event):void {
if (playerRef.hitTestPoint(playerRef.x,this.y - (playerRef.height/2)) && playerRef.x + playerRef.width > this.x && playerRef.x < this.x + this.width && !MovieClip(parent).upDown) {
MovieClip(parent).downMomentum = 0;
playerRef.y = this.y - playerRef.height;
}
if (playerRef.hitTestPoint(playerRef.x,this.y + this.height) && playerRef.x + playerRef.width > this.x && playerRef.x < this.x + this.width) {
MovieClip(parent).downMomentum = 0;
playerRef.y = this.y + this.height + MovieClip(parent).gravity;
}
if (playerRef.hitTestPoint(this.x,playerRef.y) && playerRef.y + playerRef.height > this.y && playerRef.y < this.y + this.height) {
MovieClip(parent).speed = 0;
playerRef.x = this.x - playerRef.width;
}
if (playerRef.hitTestPoint(this.x + this.width,playerRef.y) && playerRef.y + playerRef.height > this.y && playerRef.y < this.y + this.height) {
MovieClip(parent).speed = 0;
playerRef.x = this.x + this.width;
}
if (playerRef.hitTestObject(this)) {
MovieClip(parent).groundTouch = true;
} else {
MovieClip(parent).groundTouch = false;
}
}
And the jump function runs like this:
stage.addEventListener(Event.ENTER_FRAME, updates);
function updates(e:Event):void{
player.y += downMomentum;
if(!groundTouch && downMomentum < downMomCap){
downMomentum += gravity;
}
if(downMomentum > downMomCap){
downMomentum = downMomCap;
}
if(upDown && !jumping && groundTouch){
jumping = true;
jumpTimer.reset();
jumpTimer.start();
}
}
jumpTimer.addEventListener(TimerEvent.TIMER, jumpTick);
function jumpTick(e:TimerEvent):void{
if(downMomentum*-1 < downMomCap){
downMomentum -= jumpProg * jumpIncrement;
}else{
downMomentum = downMomCap * -1;
}
jumpProg -= 1;
}
jumpTimer.addEventListener(TimerEvent.TIMER_COMPLETE, jumpDone);
function jumpDone(e:TimerEvent):void{
jumpTimer.stop();
jumping = false;
jumpProg = 5;
}
I just can't find a solution to this, though I suspect it's something to do with how it checks for the player touching the platform.