System is Ubuntu 9.10, latest, kernel 2.6.31-12-generic.
Seems you are right about this not being reproducable with the MediaPro stick, however the libmediaclient.so preload affects tvheadend with regards to my other DVB-card...
I have a TT-1501-C PCI-card as my first DVB-adapter, and as far as I can tell the problems relate to tvheadend opening /dev/adapter0/demux0. No such problems when running tvheadend without the library preload.
So, in summary, to reproduce you will need a system with a "real" DVB-card, and tvheadend running with the libmediaclient.so library preloaded...
I don't have time to get more details at the moment, let me know if there is anything in particular I should do to assist you in light of this new information.
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Regards.