Any tips on removing the "pop" when flipping a image/ bone?

So on my character, sometimes the arms directions have to change- so I change them in one frame- scalex = -1, then the next frame +1. It works well, except when playing back, it "pops" out (and I think last time I tested, it shows in the game too) - probably animating it between the two scales instead of just changing it.

Example (on the arm without the sword- moved from behind the leg for visability):

Any ideas for having it just flip, without trying to animate between the 2 frames?

Awesome, thanks mfedorov, that fixed it!

I was thinking about playing with the interpolation, but the "step interpolation" is easier than playing with the curves.

Thanks!