Negative cubic-bezier values are broken on sequences and groups

When applying easing with cubic-bezier and negative value (e.g. `cubic-bezier(.2,0,1,-1)`) to animation groups or sequences the result is not as excepted. They will not show a bounce effect.
Normal animation work fine. Recognized this issue in all mayor browsers on Windows 8 (Chrome 36 and 38, Firefox 31; IE 11).

Here you can find an example for all three types: http://jsfiddle.net/u2v1L8zs/1/
