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Did you use any other filters on that or JUST anti-aliasing? Because I had that problem with some Gurren Lagann footage and now I'm curious--I had tried to use Deblock on it and it didn't help. Also, what is the script you use for anti-aliasing?
There are a lot of anti-aliasing scripts. My favorite antialiser is saa() though that is a pretty strong antialiaser meant for bad cases. You should probably resort to daa() or maa() with most SD content antialiasing. You can find saa here, whereas daa and maa are part of the animeivtc.