Unity 4.6 Mask not working in iOS

The new Mask component is not working on iOS. It is working correctly in preview mode when running on Mac or Windows, but when deployed to an actual iOS device (iPad 3rd gen, in my case) the mask is completely ignored and the children of the mask object are rendered even outside the mask.

I am on 4.6 beta 17.

Is this a bug, or am I missing something?