'Attached' bitmap cannot be zoomed too far?

programming flash
1

I’m finding there’s a limit on scaling a bitmap which has been attached to MovieClip using its attachBitmap method. For example, this will work correctly (shows a green and red square)…

import flash.display.BitmapData;
import flash.geom.Rectangle;

var bmp:BitmapData = new BitmapData(2000, 2000, false, 0x00CCCCCC);
bmp.fillRect(new Rectangle(0, 0, 10, 10), 0x00FF0000);
bmp.fillRect(new Rectangle(10, 10, 10, 10), 0x0000FF00);
_root.attachBitmap(bmp, _root.getNextHighestDepth());
_root._xscale = 409.59;
_root._yscale = 409.59;

But changing 409.59 to 409.6 for the scale makes the image disappear!

Is this a bug? Anyone seen it documented anywhere or know a workaround?

Thanks

Mark