Tvheadend

Hello,
I've installed a DVBSky T982 on an Ubuntu 14.04, I think successfully.
Since this is dual channel card, there are two individual adapters:
#ls /dev/dvb
adapter0 adapter1
The card supports DVB-T and DVB-C as well. If I select one adapter from Tvheadend GUI webpage, I can add the DVB-T frequencies for my location (Germany). The same for the other adapter.
But the other adapter should be used for DVB-C. How can I tell Tvheadend to set the type DVB-C for this adapter?
I played a bit with the configuration files in /home/hts/.hts/tvheadend. In the in the file dvbadapters/_dev_dvb_adapter1_Sit2_DVB_T2_C, I changed the line "type": "DVB-T" to "type": "DVB-C". I restarted the Tvheadend service, but usually Tvheadend resets the line back to "type": "DVB-T".
One time Tvheadend believed me, that the card can receive DVB-C, I found several channels and I also could watch a HDTV channel via cable. But after a reboot, Tvheadend unfortunately has forgotten all the DVB-C stuff :-(

Is there a way to configure Ubuntu or Tvheadend to change the DVB type of an adapter?

Best regards
Daniel

Edit:
Sorry, I forgotten to add the Tvheadend version:
Build: 3.4.28~geb79aee~trusty