Bob,  I don't have any knowledge of Aeolian organs but, as an organist,
the fact that roll 3415 turns off the Swell when the Echo is turned on
makes sense.

If the Echo can be coupled to either manual (Swell or Great) you would
likely cancel all the stops on that manual if you wanted to Echo to
play alone.  That's typically how you manage a floating division which
doesn't have its own dedicated manual.

Dale Dohler
Ann Arbor, Michigan