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I've experienced similar with the iMac. When I watch a DVD now, I reduce the size of the DVD window slightly and have chosen a textured background desktop image that shows around the edges of the DVD window. It's dark and neutral, but not darkest black. I don't see the distracting "light leaks" under these circumstances.
Not a cure, and it means a less than full screen image, but it's a solution I can live with. In fact, I quite like the "custom" look!
 
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