Hi,
I can confirm this issue and also reported this to TBS last week (hadn't seen this thread) with regard to my dual DVB-T2 card (TBS6281) and worked with them on the problem. The issue is the second adapter provided by the card being untuned on bootup and VDR start and the associated kdvb process entering the D state.
I worked around it for now by using dvbtune to tune the adapter to an initial DVB-T frequency on boot up (init script which starts before VDR), but they say they are fixing it in the next driver release.
Thanks,
Morfsta