Adding a track interrupts playing [UPnP]

Just set up a Pi with Volumio, using UPnP on an Android device with BubbleUPnP.
Everything’s fine except the following : adding anything to the playlist currently playing works, but also acts as if you hit the stop button, which is a bit annoying since it interrupts the playing of the current track, and you have to play it again from start.
I don’t have this issue when playing ‘local’ or with another networked streamer (SoTM sMS200) with same NAS, same network, same control point.
Thank you for any help or insight on that !

Thought it might be an upmpdcli issue, but it actually looks like a Volumio one :