Commit 6d1dfc3945917b507d40f1f3c1b1cf07858d18dd ('Change bits_image_fetch_pixels_convolution() to fetch just one pixel.') broke the shadows in compiz again. In contrast to a previous similar problem though, they aren't always invisible but just look more or less randomly wrong.
Do you have a screenshot of them being wrong?
Nevermind, I see what's wrong. Fixed in 93923c626f2df18e29e215410e6d4bb2f5c1616f
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