Problem with CIFilters

[Julius Eckert]

Hi,

I am implementing something like a coverflow. So I have many visual elements
in the background and one which is closer to the user and in focus.
I put a transparent layer on top of the background elements, which makes
them darker. This is very good to make the user focus more on the element in
the foreground.
I had applied additionally an backgroundFilter to this transparent layer
(CIGaussianBlur. CIBoxBlur ... tried both). This effect is so great I really
want it in my product.
The problem is that some weird lines appear when other layers are drawn in
my scene.
Did a short screencast to make this more clear:

http://www.mygnu.com/julius/temp/SFBug.mov

Has anyone an idea , why this is happening and how I can fix it?

BTW: its a quicksilver interface called "silverflow", already available as
beta on my website www.jeckert.net.tc   , freeware

Thanks in advance,
Julius