OK. Well, I'm guessing here, but it looks like you have the position recorded in your playbacks along with the colour and intensity. When you put the fader up the fixtures move to that position, when you bring it down the fixtures are released and so they go back to the default position (which is probably the same as Home).
Firstly, does it matter how the fixtures are positioned if the intensity is zero? If it is the movement when you bring the faders up that is bothering you then try changing the trigger level or press the Go button on the playback before raising the fader.
If that doesn't work for you then there's more than one way out of it but first you need to remove the position information from your playbacks. You can do this with update/remove or by just deleting them and recording them again without pan/tilt parameters.
If you only need the fixtures in one position you could set that position as the default. Another option is to record the position on another playback and keep that up. There's also the option to disable Release on Lower but this will keep the colour as well - at least until it is overridden by another playback.
Or, you could wait until the Z88 people give you a more authoritative response - I'm an FLX user and often recommend solutions only available on that console (I have checked the S48 manual this time though.)