Blurred arrows in TreeView

I notices an annoying issue. Arrows in treeviewitems are blurred with comparing to non-styled Treeview

MA
![image](https://cloud.githubusercontent.com/assets/6085009/7387013/41d8423a-ee62-11e4-9140-65e2d140e0ea.png)
native:
![image](https://cloud.githubusercontent.com/assets/6085009/7387022/5ff3d7c0-ee62-11e4-9468-bd531384f27e.png)
