Tvheadend

I have a very strange problem that every saturday a recording on a specific channel (RTL2 on Astra 19.2) drops the video stream about 45 minutes into the recording. Audio keeps recording and subsequent overlapping recordings on this channel only have audio.

Here's my setup:
LNB Inverto IDLI-8CHE20 (SAT>IP)
Client1: TVheadend 3.9.1743~ga510248 compiled from source on Debian Wheezy on a Cubox-i4pro (armv7)
Client2: DVBViewer Recording Service on Windows7 64Bit (AMD Phenom II X4)

I set up 4 "tuners" each for both machines.
During the time that the video stream stops there's no other VDR activity (other recordings staring/stopping) on either machine.
Both machines record the same channel but do not start exactly at the same time. TVHeadend uses an autorec for the show ("Warehouse 13") and DVBViewer is set up manually from EPG.
TVHeadend has dropped this recording for several weeks now and the DVBViewer had no problems at all.

For the past week I set up recordings on RTL2 every day from 20:15 to after the usual dropout time but all recordings except the saturday recording were OK.
The thing is that the channel does not recover the video stream unless it is shut off and retuned.

Here's the channel setup for TVHeadend:
Frequency 12187500,
Symbolrate 27500000,
Polarisation H,
Modulation QPSK,
FEC 3/4,
Rolloff 35
Character Set was unset, now changed to AUTO
PMT Descriptor 0x06 disabled
Pilot AUTO

DVBViewer uses the same settings except the frequency is 12187000 but this could just be a granularity thing in the DVBViewer.

Does anybody have an idea what might be going on here and what i could do to debug this?

Regards
Aydan