Masked Object flicker on Unity 4.6 (final) UI (webplayer)

Hi,
we waited for the final release to understand if it was a problem of the beta builds, but the problem persists.

We're using Unity 4.6 UI system with a masked object and the entire object starts to flicker, as you can see from the following screen capture.

https://www.dropbox.com/s/6dy5rcx3993acg4/bug-flicker-unity-4_6.mp4?dl=0

The flicker is present in every browser (safari, chrome or FF latest versions) on Mac OS X 10.10