If you are talking about Audio Tracks, then what you are doing with the nodes is to add CC7 Volumn data to your track as can be seen from the Event List. This indeed acts exactly as you describe. I would be much happier if you could separate the overall mix volumn from the alterations caused by Node changes. This would enable changes made to the overall track volumn in the mix to be reflected by relative changes to the node values. In Midi, this is the relationship which CC11 Expression has with CC7 Volumn.

Maybe, you could allocate the track(s) to Groups in the Mixer where you can then change the Group Volumn in relation to other Groups and retain the track Nodes without change.

I hope this is of some help.