Hmmmm....I am not sure about this one. I use NxStage at home, and my nurse told me that the only fluid my machine pulls is my rinse back and whatever I set the UF to remove. Technically that means that I do remove fluid, even if the UF is off, but only the amount that I am given back at the end of treatment. I have never used any other machine, but I am sure someone here will give you a better answer. It would be a plus if the NxStage cycler would just take off whatever it needed to, but it definitely does not. Hope you find the answer. Nothing worse than feeling lousy after treatment, especially if it is from pulling fluid you don't need to!
This also happens with NxStage. Our current cycler regularly pulls 300-600ml extra. It seems to be very cycler-dependent - the last cycler didn't pull nearly as much. I'm not sure if time is also a factor, as he runs for about 8 hours. I just know that if he has, say, 1L to come off, and he drinks maybe 500ml during treatment, he'll generally come out about even. If he falls asleep early and doesn't drink much, I'll reduce the UF so he's not overdrawn.
Do you use the same machine every time? If you do, I'd demand to have the machine looked at. You shouldn't have so much taken off while in minimum, and if I were you, until it was fixed, I'd be asking to be taken off whenever you start to feel the cramping come on