I think you just have to see this as an (Autodesk) choice. I expect that the first reference plane you add will be the 'dominant' one
Revit, behind the scenes, tend to add some internal constraints and try to 'predict' your intentions. So when you add the parameter it moves only one line.
You can see this process also often when you add between those reference lines an extrusion (e.g. box). Quite often the extrusion will size based on the reference planes, this while you have not constrained/locked it to the reference planes.
Sometimes these constraints can be little bit unpredictable and cause unexpected behavior. The solution is simple, constrain things like you need them to behave.
Louis
Please mention Revit version, especially when uploading Revit files.
