Tvheadend

I've noticed a strange behaviour after adding a Cine S2 card to my system.

I had the following cards:
3 x Picostick 74E
1 x WinTV-Nova-T500

And I have some IPTV channels mapped too.

And then I added the Cine S2. I did some experiments (the rotor is not working for me), and I noticed that if I have SAT channels mapped, the frontends (Raspberry Pi with Openelec) tend to slow down and the zapping time increases dramatically from 2-3 seconds to > 10s.
Is this known bug? Actually the same thing happens when using the PC as frontend.
After deleting the channels and disabling the Cine S2, normal zapping speed is restored.