Well, it's equally unlikely that a MediaPortal bug would only affect one program on one channel.
It is much more likely to be MP bug if only a specific channel is affected. If there is some issue with the signal / tv card at least all of the channels that are on the same mux should be affected (in most cases all the muxes are affected). When some specific channel is affected then the stream is proably containing something that trips the TsReader (or video decoder, but it is less likely).