firefly wigs out if you remove a source that is referenced in a graph

[Roguelazer]

If you remove a source that is referenced in a graph (for example, removing a directory from ganglia), any attempts to edit that graph will fail (so you have to completely recreate the graph). I think this is because the frontend gets a 500 back from the data server, but I'm not sure why, for example, you can't just delete the offending entry from the source list.