Flash graphics glitch with alpha transparencies: any ideas what could be going wrong?

Question

Hey folks, this forum has found me loads of answers in the
past through various searches but now it's time for me to enquire
about something myself...
Here's a bit of graphics I'm going to be using as part of a
larger project:
http://www.stucox.co.uk/file_dump/LogoGlitch.html
You'll see that as the mask for the logo at the top seems to
bite a chunk out of the mask on the arrows below (they've got an
alpha mask on them to make them fade towards the top)... this is
just a graphics glitch as if you get it to redraw that frame, it
redraws fine.
What could cause this? it's almost as if the two masks (the
one on the logo and the one on the arrows) are adding/subtracting
together, even though they're in totally different layers of
heirarchy, have different instance names, etc
I know that the issue is the masks as if i disable either one
or the other, it renders fine. I've also noticed similar things in
other areas of my graphics with two coinciding masks causing
glitches.
The one solution I've found (short of removing my
transparency, but I want to keep that as part of the design!) is to
make the movieclip containing all of the arrows to move very slowly
(at least one pixel per frame seems to do it), which seems to stop
the glitching - no idea why, other than that it might be forcing it
to redraw properly?
I've tried playing around with the bitmap caching on just
about every movie clip in the movie and all sorts...
Any thoughts?

Answer 1

Thanks for the reply, sorry it's taken me a while to get back
on.
This is all going to be over the top of a bitmap background.
No, you're right - this doesn't come anywhere near 10 alpha layers.
The arrows are just bezier shapes I've drawn myself.
And yeah, I can't really afford to make it low quality (I
think the only reason that works is it then ignores alpha
transparency), this is all going to be an "impressive" minsite for
a big clubbing event in London!
Obviously I can just tone down some of the animation a bit -
make the arrows part of the bitmap background rather than tweening
them on screen etc, but I'd really like to understand what's going
wrong here to try and avoid it in the future!