Create a second depth graph from same file puts 2 graphs with one label

Make a depth graph. Make a second depth graph from the same file. I get a 'joined' type track with 1 label but 2 graphs. Cannot be split, one graph line cannot be deleted - I tried.

NOTE: Hiral says this is not a bug, but working as intended? Ann, do you know why? Can we change this so making a second depth graph from the same file is just like copying it?