A new report discusses these problems (a longer journal article is forthcoming). For those who rely on secondary data in general and ANES data in particular to examine political knowledge, this brief report is worth the read. The problem comes down to this -- coding for wrong answers included ones that should have been categorized as correct. In asking what office does William Rhenquist hold (he was chief justice of the U.S. Supreme Court at the time), listed as wrong were such responses as "supreme court justice head honcho" and "supreme court justice, head." Should have been listed as correct.
To their credit, the fine folks at ANES have worked hard to understand and address the problem, even providing access to open-ended materials so people can more dutifully check whether a political knowledge answer is indeed incorrect.
All of us should appreciate the work of the report authors, James L. Gibson and Gregory A. Caldeira.