"is MovieClip" is true, yet compiler insists it is not and throws Error #1034: Type Coercion failed? (AS3) - actionscript-3

Question

I have in my library, various food icons converted and linked as MovieClips which i add to the scene dynamically. I'm trying to move them from one container to another. Containers are also dynamically added MovieClips.
I've been trying to move these icons who are "MovieClip extended class" instances to another MovieClip as child, by drag and drop, yet currentTarget in drop(it is fine in drag) is not recognised as MovieClip even with "currentTarget as MovieClip" and compiler throws error. Every trace indicates that it is indeed a MovieClip though. I'm at my wits end.
The "plate.addChild(mc);" is causing the error during dropping into the "plate" from "shelves".
The .fla file: https://1drv.ms/u/s!ApqQOqYhGvWHget1A4YRqyzT3a9BEQ?e=9UJB0R
import flash.display.Sprite;
import flash.display.MovieClip;
/*;
choValues = {
"apple": 15,
"bakedBeans": 15,
"chickenLeg": 0,
"chickenNuggets": 15,
"cornOnTheCob": 15,
"egg": 0,
"grapes": 5,
"hamburger": 30,
"milkFull": 24,
"juiceFull": 30,
"juiceHalf": 15,
"saltineCrackers": 5,
"orange": 15,
"tomato": 5
}*/
var foodNames:Array = new Array();
var choValues:Array = new Array();
var options:Array = new Array();
var index:Array = new Array();
var shelves:MovieClip = new Shelves();
var plate:MovieClip = new Plate();
var plateSlots:Array = [0,0,0,0];
var iconSize:Array = new Array();
trace(stage.stageWidth);
trace(stage.stageHeight);
var relativeWidth:Number = stage.stageWidth/32;
var relativeHeight:Number = stage.stageHeight/32;
trace("shelves");
trace(shelves.x = relativeWidth*4 );
trace(shelves.y = relativeHeight*8);
trace(shelves.width = relativeWidth*10);
trace(shelves.height = relativeHeight*14);
stage.addChildAt(shelves,1);
trace("plate");
plate.instanceName = "plate";
trace(plate.x = relativeWidth*15 );
trace(plate.y = relativeHeight*8);
trace(plate.width = relativeWidth*10);
trace(plate.height = relativeHeight*14);
plate.name = "plate";
stage.addChildAt(plate,0);
trace("plate.name "+ plate.name);
/*var fruit = new orange;
trace("fruit");
trace(fruit.x = plate.width/2);
trace(fruit.y = plate.height/2);
//trace(plateSlots.width = plate.width/2);
//trace(plateSlots.height = plate.height/2);*/
//plate.addChild(fruit);
function drag (e:MouseEvent):void //find the slot
{
e.currentTarget.startDrag();
trace("drag "+e.currentTarget.name);
trace("Classname "+ getQualifiedClassName(e.currentTarget));
}
function drop (e:MouseEvent):void
{
e.currentTarget.stopDrag();
trace("drop Classname "+ getQualifiedClassName(e.currentTarget));
trace("drop name "+ (e.currentTarget.name));
//if(e.currentTarget.dropTarget !=null)
//if(e.currentTarget.dropTarget.parent !=null)
//if(e.currentTarget.dropTarget.parent.parent != null)
try{if (e.currentTarget.dropTarget.parent.parent.name == "plate")
{
trace("currentTarget is "+e.currentTarget);
var mc:MovieClip = MovieClip(e.currentTarget);
trace(mc);
trace("mc is movieClip?" + (mc is MovieClip));
trace("is plate");
for (var i=0; i<4; i++)
{
if (plateSlots[i] == 0)
{
trace(mc);
//shelves.removeChild(mc);
plate.addChild(mc);
//e.currentTarget.width = iconSize[0];
//e.currentTarget.height = iconSize[1];
trace(mc.x = plate.width/6 + ((i%2)*plate.width/8));
trace(mc.y = plate.height/6 + ((i<2 ? 0:1)*plate.height/4));
plateSlots[i] = 1;
mc.slot = i;
return;
}
}
}
else{
shelves.addChild(e.currentTarget as MovieClip);
e.currentTarget.x = e.currentTarget.oldX;
e.currentTarget.y = e.currentTarget.oldY;
}
}
catch(e:Error){}
shelves.addChild(e.currentTarget as MovieClip);
e.currentTarget.x = e.currentTarget.oldX;
e.currentTarget.y = e.currentTarget.oldY;
}
function randomize ( a : *, b : * ) : int {
return ( Math.random() > .5 ) ? 1 : -1;
}
foodNames.push(
"apple","bakedBeans","chickenLeg",
"chickenNuggets","cornOnTheCob","egg",
"grapes","hamburger","milkFull",
"juiceFull","juiceHalf","saltineCrackers",
"orange","tomato"
)
choValues.push(
15,15,0,
15,15,0,
5,30,24,
30,15,5,
15,5
)
for (var i:int=1; i<foodNames.length; i++)
{
index.push(i);
}
index.sort(randomize);
trace(index);
for(i=0; i<8; i++)
{
options[index[i]] = new (getDefinitionByName(foodNames[index[i]]));
trace("class "+getDefinitionByName(foodNames[index[i]]));
options[index[i]].addEventListener(MouseEvent.MOUSE_DOWN, drag);
options[index[i]].addEventListener(MouseEvent.MOUSE_UP, drop);
options[index[i]].CHO = choValues[i];
options[index[i]].x += ( (2*(i%4)) +1 ) *(shelves.width /10);
options[index[i]].y = ( ( i<4 ) ? 17 : 37 )*(shelves.height/64);
options[index[i]].oldX = options[index[i]].x;
options[index[i]].oldY = options[index[i]].y;
shelves.addChild(options[index[i]]);
}
//iconSize[0] = options[index[0]].width;
//iconSize[1] = options[index[0]].height;
stop();