Manu,

The chip you have is from a very early batch.  The fault you are probably
seeing is a race condition.  This problem was completely eliminated in June
(before we launched mass production).  The sample you have is from a
preproduction engineering batch (not for commercial sale).  The antidote is
to obtain a new card from KNC1 with a later batch number (your IC probably
has C1L marked at the top, get one with C2L to be sure or > MLT 22 624)...

The symptoms are as follows.

The IC performs perfectly in DVB-S modes (all modes, all symbol rates).
When in DVB-S2 depending on temperature, supply voltage and carrier to noise
ratio the device may lose either FEC lock OR the FEC may remain locked but
the packet delineator (and thus transport stream) outputs errors.
Heating or cooling the device (say with freezer spray / hair drier) will
bring the device back to correct operation (you may need to relaunch an
acquisition).

If a blast of hot or cold does not solve your problems let me know.

Regards Peter