Hi.
Move on Dark can only work when there is a cue in-between where the fixture is dark and the desk can prep the new position or colour etc for the next time it's used. If your cues are consecutive then there is no opportunity for the desk to do "move on dark". Maybe you were expecting the desk to "dark" the fixture, move it, then relight it? This is not move on dark. If you wanted that, either you would need to programme that specifically or some moving lights can "dark" themselves when moving (I'm not sure if they relight afterwards though!).
If the fixture fades out to home, this sounds like a programming issue in that you've not told the fixture what to do in that subsequent cue.
There was another user recently who had a similar query but with zoom on a fixture. I wonder if my reply might help (mentally change "zoom" to "position" when reading my comments!).
If this doesn't help then maybe you could explain a little more or even upload your showfile?
I don't know where the Zero88 folk are at the moment, maybe there is a trade show on. Your query should be something we users can help you out with if you can work with us a little.
There are a great set of Training Videos for the FLX consoles. When you get time I would watch through them. If you want to jump in on Move on Dark, here is the video that might help you out:
Here's the whole playlist on YouTube: