unable to mirror animation by scale -1 in 4.6.1f

I used to mirror generic animation by scale (-1,0,0) in 4.5.5f, (if animation clip has an unconstant scale curve). but when updated to 4.6.1f, it doesn't work any more. my hole game is base on this. what should I do?

We did change how the scale is blended is 4.6 but I don't think it could be related because it does only affect the blending while in a transition .

Ca you please log a bug with your project?