writing the volume mix

I have three layers, which I want to mix live and record at the same time. So, I am a midi controller (nanokontrol2), and I have each of the layers on own slide of the controller. However the problem is that layer1 doesn’t like to keep my mixed volume in the place where I moved it (with the slider). It jumps back to the center volume; the same which was there in the beginning! I don’t get it, why it’s jumping back there. Layer2&3 are not acting like that. I don’t have any other volume or gain settings recorded to that track, so it’s very strange.

using Cubase5