Issue with volume control when multiple Shairport-Sync instances are grouped

[killerlife]

Description

I am running multiple instances of Shairport Sync on a Linux machine using Docker. Volume control behaves differently depending on whether a single instance or multiple instances are connected from the phone.

Observed behavior

<1>When the phone app connects to only one Shairport-Sync instance, changing the volume from the Shairport-Sync side correctly updates the volume displayed in the phone app.

<2>When the phone app connects to multiple Shairport-Sync instances in a group, changing the volume from one Shairport-Sync instance causes the volume of all grouped players in the phone app to change.

<3>The resulting volume values shown in the phone app are not consistent with the value set from Shairport-Sync.

How the volume is being changed

I am using the command from sample.dbus.commands:
dbus-send --print-reply --system
--dest=org.gnome.ShairportSync
/org/gnome/ShairportSync
org.freedesktop.DBus.Properties.Set
string:org.gnome.ShairportSync
string:Volume
variant:double:-10.0

Question

<1>How can I further diagnose or debug this behavior?

<2>Is this expected behavior when multiple AirPlay receivers are grouped?

<3>Is there a recommended way to control volume via D-Bus in this multi-instance setup?

Any suggestions on how to locate the root cause or resolve this issue would be greatly appreciated.

[mikebrady]

Thanks for the interesting post, but this would be better dealt with as an Issue. Could you post it as a new issue, please?

[killerlife]

OK, I was posted as a new issue.