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CSS animations rely on unspecified behavior
Some of the Sencha Animator demos look wrong in recent WebKit nightly builds. For example, in http://dev.sencha.com/animator/demos/pageflip/, the pages look semi-transparent during the entire page turn animation.
I think the animations are relying on behavior that was changed as a result of fixing this bug:
I see animations with opacity: 0 for only the first few keyframes (say 0% and 10%) ,and none of the later ones. What WebKit used to do is animate opacity from 0 to 1 from the 10% to the next keyframe. After that bug was fixed, opacity now animates from 0 at 10% to 1 at the 100% keyframe.
To work around this behavior change, you should supply a value for opacity in every keyframe.