I am getting there quite fast with FS already, quite a piece of software

I have one problem though :
I have set up my LED's for different colors by making 1 step sequences for each color, adding them one and one to a cue and connecting that cue to submasters. The submaster intensity channels is then controlled by a fader on my BCF2000's. This works fine, fading the LED's up from 0 to full with he fader on the BCF2000, but ONLY if I have the Submaster-window open !!! If I don't open the submaster window whet happens is that when I start moving the fader the lights come on, proportional to the fader but when I stop moving it at, let's say 20% after about half a second or so it jumps to full intensity (the LED, not the fader). If I then grab the fader and move it the lights again follow the fader but when I stop moving it, BANG, ip to 100% again.
Then I open the submaster-window and it works again.
What am I missing here, or is this the way it works for some reason ?
Thank You
Magnus