I've just experimented lately with Qtractor's busses and routings. If I wanted to pass signal from one Qtractor bus to another I used some jack client in between (ie. jack_simple_client or jalv with some simple plugin that's doing nothing to the signal). So if that's what you are up to you could try that approach as well. Master bus was a bit exceptional in this regard - accepted signal from other busses without any intermediate clients.
I've just experimented lately with Qtractor's busses and routings. If I wanted to pass signal from one Qtractor bus to another I used some jack client in between (ie. jack_simple_client or jalv with some simple plugin that's doing nothing to the signal). So if that's what you are up to you could try that approach as well. Master bus was a bit exceptional in this regard - accepted signal from other busses without any intermediate clients.