Puzzling vector mask clipping path fringe issue

[ronv...@gmail.com]

Hi,
I have a PSD document that is basically a group of vector masks. These
layers with their associated masks are arranged in such a way that any
image can be loaded into this file and it will take on the appearance
of a jigsaw puzzle. You can see the results of a flower loaded here:

http://picasaweb.google.com/ronviers/PuzzleProject/photo#5000493209136594962

Or if you cannot make out the detail for the purposes of this question
you can open it in your browser here:

http://lh5.google.com/image/ronviers/RWVSFHhXABI/AAAAAAAAAY0/ni8mK_0yYoc/Puzzle%20for%20web.jpg?imgdl=1

Anyway, the way this is supposed to work is that an arbitrary image is
loaded into the PSD as the 'Puzzle' layer. You can see the basic
layer structure and the 'Puzzle' layer, which is temporarily a
flower, here:

http://picasaweb.google.com/ronviers/PuzzleProject/photo#5000496064448626706

There is also a 'Pieces' group filled with the individual vector
masks with clipping paths for each piece. You can see the pieces group
here:

http://picasaweb.google.com/ronviers/PuzzleProject/photo#5000496537233129490

Notice how some of the pieces are red. Once the image that is to be
used at the 'Puzzle' layer is loaded into the document the pieces
layers (pieces) that are to be uses are changed to red so they can be
selected manually later. Finally there is an 'Archive' group used
to contain the source for the paths and two styles. The style source
layers are used to customize the appearance of the pieces then those
styles are pasted en mass onto either the pieces that are to be visible
or the ones to be invisible. You can see the archive group contents
here:

http://picasaweb.google.com/ronviers/PuzzleProject/photo#5000497057332723730

Now for the question. The way this is supposed to work is I go through
and do a 'Knockout Deep' to background to all the pieces that are
to be invisible. Btw, my original idea was that I would simply make
invisible (click on the layer eye) the pieces to get rid of them but
reality set in and I had to come up with the cumbersome 'style' pasting
technique. Back to the question. After I do a knockout to background
the image is left with a slight outline of each piece. You should be
able to see it on any of the pictures in the album. I have tried and
tried to get rid of that outline - for purposes of flexibility I
intentionally never stroked any of the paths. Can anyone tell me where
this fringe or outline comes from and how to get rid of it?
And a second question, since this is my first time to use vectors, is
that if anyone has any suggestions on how to better approach this
project or tips to handle it they would be greatly appreciated.

Thanks,
Ron