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yes, ive noticed it too, on several occasions. usually pressing pause/play or toggling that taskbar a few times fixes it. not sure what causes it either. im not jailbroken (new ipad isn't jailbreakable anyway yet) so it must be a bug. doesn't bother me immensely though, i can adjust the volume still or with the rockers, so it doesnt really impede anything, just graphically it looks kind of weird.
 
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