Starling DisplayObject mask bug with browser page zoom != 100%


I found strange things with masks.

var mcScrollView - is empty Sprite from GUI constructor (see on picture)

var visibleRect = new Rectangle(0, 0, 530, 350);
var mcContainer = new Sprite();


var quad:Quad = new Quad(visibleRect.width, visibleRect.height, 0x808080);
quad.x = visibleRect.x;
quad.y = visibleRect.y;
mcScrollView.mask = quad;
// _mcScrollView.addChildAt(quad, 0); // to test size and position of Quad

mcContainer.addChild(new FaqSlot());
mcContainer.addChild(new FaqSlot());
mcContainer.addChild(new FaqSlot());
code to implement scrolling content (where I change _mcContainer.y)

It works fine if 100% browser zoom:

150% browser zoom:

50% browser zoom:

If I add same Quad as simple child (not as mask) - it’s size and position are ok with different browser zoom:

You need to know, that I update Starling viewport size and position and Starling stageWidth|stageHeight every EVENT_RESIZE to cover all available browser space.
But I don’t think it matters because we work in logical Starling coordinate system.

Any ideas?)