When the system log appender writes to the stdout stream, sometimes the write fails and the fail bit gets set on the stream. I can reproduce this just by starting mongod – the first write to stdout that typically fails is the one from the HostnameCanonicalization thread saying that it is starting up.
The problem occurs even with binaries built on 10.8 and run on 10.10. The errno set after the stream goes bad seems to be either "0" or "2".