Race Condition when creating Aux-Sends?

Hi, it's me again, the old fart with slow computers and big Qtractor projects.

Yesterday I ran into a little issue when I wanted to do some latency measurements with jack_iodelay. The steps were:

1.) connect jack_iodelay's audio out to an input bus.

2.) Add into this input bus an Aux-Send to an output bus named "Common". The "Common" output bus has already an Aux-Send to the Master bus.
-> That works "kinda". The signal from jack_iodelay is audible. But only in the "Common" bus the meter shows a signal. In the Master bus the meter shows nothing and plugins don't affect/process the signal.

3.) When I switch the Aux Send in the "Common" bus to none and back to Master, then everything works as expected.

It's not reproducable in a fresh, minimal session but in an existing big project, so I could make a screencast.

EDIT:
It is reproducable in a fresh session, e.g. in the attached sample session.