I trust you mean "BLANK CARD FEED" and not "REJECT_BLANKCARD". The BLANK CARD FEED message is not generated by GEMS. It happens when the AccuVote gets no timing marks at all from the reader. Feed a completely blank peice of paper into the AccuVote and you'll see the message every time.
It has been a while, but I saw this myself in Pima and brought it up back in Nov 98. I would be surprised if it doesn't happen in King all the time, but then I wouldn't know much about that. Its the reader or the firmware, and my bet for a long time has been on the former. My pet theory is that when it happens in precinct count we never hear about it since a poll worker would just shrug and refeed, and it always seems to take the second time.