Thanks Geoff. I tried this and instead of copying, it moved the envelope to the destination buss.
IOW - I copied the buss envelope, and pasted it into an audio track (its then in the origin buss and the
audio track). I then copied the envelope in the audio track and pasted it into the destination buss.
It then appeared in the destination buss, but disappeared from the origin buss.
Is this some known SONAR problem?