UI problem with mask

I am using one and it has a material. When I use the mask he does not hide it. Anyone know how to solve? This problem did not give in beta20 (but not only that it gave).

Have you tried to switch the option “Show mask graphic” from the UI Mask component?

Check this video, it will explain what does the show mask graphic does.

http://unity3d.com/learn/tutorials/modules/beginner/ui/ui-mask

Regards.