Sprite layers are disappearing in AS3 drawing code - actionscript-3

Question

I'm building a custom painting application, and I'm running into a problem where the layers I'm adding to the canvas are disappearing after 24 layers get added.
Here is my code for the drawing tools:
//=====================================================================================================================================
// DRAWING FUNCTIONS
//-------------------------------------------------------------------------------------------------------------------------------------
protected function onMouseDown_canvas( evt:MouseEvent ):void
{
var p:Point = new Point( _realView.mouseX, _realView.mouseY );
_log.log( "CanvasViewController :: onMouseDown_canvas() - mouse:" + p );
_realView.addEventListener( MouseEvent.MOUSE_UP, onMouseUp_canvas );
_realView.addEventListener( MouseEvent.MOUSE_OUT, onMouseOut_canvas );
_realView.addEventListener( MouseEvent.MOUSE_MOVE, onMouseMove_canvas );
_currentLayer = new Sprite();
_currentLayer.mouseEnabled = false;
_realView.mcContainer.addChild( _currentLayer );
_$clearFirstBrushStroke = false;
switch( _$tool )
{
case ToolType.ERASER:
case ToolType.BRUSH:
case ToolType.PENCIL:
_currentLayer.graphics.beginFill(
( _$tool == ToolType.ERASER ? 0xffffff : _$color ),
( _$tool == ToolType.BRUSH ? .4 : 1 )
);
_currentLayer.graphics.drawCircle( p.x, p.y, _$toolSize/2 )
_currentLayer.graphics.endFill();
_firstPoint = p;
_$clearFirstBrushStroke = true;
if( _$tool == ToolType.BRUSH )
_currentLayer.filters = [ new BlurFilter( 3, 3, 2 ) ];
break;
case ToolType.BRUSH2:
drawGlitter( _currentLayer.graphics, p );
break;
}
}
//-------------------------------------------------------------------------------------------------------------------------------------
protected function onMouseUp_canvas( evt:MouseEvent ):void
{
var p:Point = new Point( _realView.mouseX, _realView.mouseY );
_log.log( "CanvasViewController :: onMouseUp_canvas() - mouse:" + p );
endDrawing();
}
//-------------------------------------------------------------------------------------------------------------------------------------
protected function onMouseMove_canvas( evt:MouseEvent ):void
{
var p:Point = new Point( _realView.mouseX, _realView.mouseY );
switch( _$tool )
{
case ToolType.ERASER:
case ToolType.BRUSH:
case ToolType.PENCIL:
if( _$clearFirstBrushStroke )
{
_$clearFirstBrushStroke = false;
_currentLayer.graphics.clear();
_currentLayer.graphics.lineStyle(
_$toolSize,
( _$tool == ToolType.ERASER ? 0xffffff : _$color ),
( _$tool == ToolType.BRUSH ? .4 : 1 ),
true,
LineScaleMode.NORMAL,
CapsStyle.ROUND,
JointStyle.ROUND
);
_currentLayer.graphics.moveTo( _firstPoint.x, _firstPoint.y );
}
_currentLayer.graphics.lineTo( p.x, p.y );
break;
case ToolType.BRUSH2:
drawGlitter( _currentLayer.graphics, p );
break;
}
}
//-------------------------------------------------------------------------------------------------------------------------------------
protected function onMouseOut_canvas( evt:MouseEvent ):void
{
var p:Point = new Point( _realView.mouseX, _realView.mouseY );
_log.log( "CanvasViewController :: onMouseOut_canvas() - mouse:" + p );
endDrawing();
}
//-------------------------------------------------------------------------------------------------------------------------------------
protected function endDrawing():void
{
var p:Point = new Point( _realView.mouseX, _realView.mouseY );
_log.log( "CanvasViewController :: endDrawing() - mouse:" + p );
_realView.removeEventListener( MouseEvent.MOUSE_UP, onMouseUp_canvas );
_realView.removeEventListener( MouseEvent.MOUSE_OUT, onMouseOut_canvas );
_realView.removeEventListener( MouseEvent.MOUSE_MOVE, onMouseMove_canvas );
var bmd:BitmapData = new BitmapData( _realView.width, _realView.height, true, 0x00000000 );
bmd.draw( _currentLayer );
var bmp:Bitmap = new Bitmap( bmd, "auto", true );
_realView.mcContainer.removeChild( _currentLayer );
_realView.mcContainer.addChild( bmp );
_currentLayer = null;
_log.log( " numChildren:" + _realView.mcContainer.numChildren );
}
//-------------------------------------------------------------------------------------------------------------------------------------
protected function drawGlitter( g:Graphics, c:Point, $glitterSize:Number = 2, $density:Number = .5 ):void
{
var $startAngle:Number = NewMath.Random( 0, Math.PI*2 );
var $stepAngle:Number = $startAngle / ( $density * _$toolSize );
for( var $i:int = 0; $i < ( $density * _$toolSize ); $i++ )
{
var $a:Number = $startAngle + ( $i * $stepAngle );
var $r:Number = NewMath.Random( 0, _$toolSize / 2 );
var p:Point = new Point( c.x + Math.cos( $a ) * $r, c.y + Math.sin( $a ) * $r );
g.beginFill( _$color, 1 );
g.drawCircle( p.x, p.y, $glitterSize / 2 );
g.endFill();
}
}
numChildren continues to grow, but once it hits 24 layers in that container, the first layer gets deleted or goes invisible or something. at 25 layers, the second layer disappears, etc.
See this in action here: http://dev.option5.net/CAUS/CAUS14002/index.html
Could it be a masking issue? Can only so many layers be masked : _realView.mcContainer (where new layers are added) is masked by _realView.mcMask?