System doesn't handle multiple variables with single variable units case

[ndebuhr]

The approach to "Variable" display is odd. So two "Variable Units" can be selected. However in these cases if there are multiple data series selected with the same Variable Units, then only one of the Variables is selected of the two. In the image example, we have "Snow water equivalent (millimeter)" and "Snow depth (millimeter)" selected, and the plot shows on the y1 sxis "Snow depth (millimeter)". It seems like showing both variables or none of the variables (just the shared variable unit) would be more clear in these cases.