Tvheadend

I am a new TVHeadend (TVH) user from the Netherlands and everything works fine so far except one thing.

I installed TVH (V4.2.1-7~g4d4bf14) on a fresh Lubuntu 16.10 installation. I use a Digital Everywhere FloppyDTV card over firewire. All (30) DVB-C channels are unencrypted and I have no CAM module. My problem is with 3 HD channels taken from the same mux. When I record (pass profile) or view (htsp to Kodi) any first of these 3 HD channels TVH gives both video and audio streams. All fine so far. But when I add recording or watching the second HD channel from that same mux, I get video, but no audio.

I also tested a parallel recording for 2 HD channels from that same mux. Always the recording that starts first has video & audio and the second (or third) never has audio.
When I repeat this test on a mux that has SD channels, both parrallel recordings have video & audio.

What am I missing or doing wrong?

I have a dual-tuner setup (but for this test took out one tuner) and as workaround tried to convince TVH, to never use a tuner for more than one subscription, but even if I enter "Free subscription weight = 1" in the tuner parameters screen, it will reuse the first tuner to deliver the second HD channel by adding a second subscription to the tuner. Which conceptually makes sense to me, as the tuner is already tuned to the right mux. But without audio for the second channel not of any use to me.

Thanks for any thoughts,
BB