I've seen motion interpolation algorithms on multiple brands of televisions stutter. Sometimes, it'll agree with the source, and sometimes it won't. Netflix, for example: on my Roku 2 XS, stutter city. From my BDP-S790, smooth as silk, no stutter whatsoever. As soon as I ditched my Roku 2 XS I was able to re-enable my cherished Motionflow Standard/Auto 1 without the deleterious side-effect I experienced with the Roku 2 XS. Back to enjoying Netflix as I prefer it, soap opera effect and all.
For those with Sony TV's, when your source causes stuttering when Motionflow/Auto1 is enabled, you can keep it enabled, just use Cinemotion: Auto 2. It'll at least give you a little sliver of the motion interpolation you're after, without the stutter, at least -- without the stutter that we're talking about here.