I thought they fixed this. Had a guy do it to me on back to back pitches. The runner didn't stumble like they showed in the stream.
Also depends on the runners attributes... I don't think the stumble is as prominent for someone like Rickey Henderson for example... the slower runners and/or guys that have a lower steal rating probably have a more visible stumble and as someone above stated it might only be during pitch outs but I'm thinking it happens at all times when a runner tries to go back to first.