Glad you got it working.
FYI, usually--but not always--the masks will look correct in the normal display. If your masking does not look right in the display, try disabling GPU Acceleration in the Display Options. If you still see problems, try also disabling Enable GPU in the Preferences. Obviously, Masking should be enabled in the Display Options.
However, this won't always correct the issue. I think some masking situations simply won't look correct in the display no matter what you do, but they can look correct in the render. For example, in two of the characters I had set up at work, when they turn their heads, one of the eyes is supposed to get clipped by a head shape mask. But what happens is that the 'exiting' eye will remain visible outside the head, even though the pupil will get masked by the head shape. It's really not that a big deal though--we can still animate the head and eyes properly and it will render correctly, so we just ignore the 'floating eye' error.
I know the error has to do with how I nested the eye and head masks. Now that I'm thinking about it, when I find the time, I should revisit these characters and see if it's possible to improve this.
But, anyway, so long as the error doesn't affect your ability to animate and properly render the scene, try not to obsess over it too much. It's more important to get your projects done.
G.