"No input detected" after some channel switching

Hello,

I have a "Philips TDA10086 DVB-S" card and it shows a pretty strange behaviour:
When scanning for services, it gets input for a couple of channels (4 channels are mapped, ~20 fail because of encryption), then all other mappings fail with "No input detected".

Restarting tvheadend helps, i.e. the card gets some more input ... and then again all mappings fail with "No input detected".