Digital Waveform Graph refuses to edit Bus names

I am trying to display digital waveforms on graph whose lines are grouped. It looks like the functionality exists to group the lines into "Buses". There appears to be a way to rename each Bus from its default "Bus 0, Bus 1, etc." since there is an Express VI called "Group Digital Signals" that does it. It looks like the express VI is editing the attributes on the waveforms in order to rename the Buses. The attributes are NI_ChannelName for the Bus and NI_LineNames for the lines that make up the bus.

When I code it, the Line Names are renamed according to what I want, but the Bus names remain default Bus 0, Bus 1, etc. Is there something I must do to rename the Buses?

(see attached VI)

Thanks,

Dan