Strange failure modes for voter sign-in

I spend a lot of time thinking about (and whining about) problems in electronic voting systems. But yesterday's Montgomery County (Maryland) election had a new twist to failures, not in the electronic voting system but in the system used by voters to check in at the polls. According to the Washington Post, "The state's list inadvertently marked as absentee the names of voters with a home address that begins with the number five. Election judges kept track of those who showed up to vote today in handwritten lists. And to ensure that voters only cast one ballot, election officials said they planned to compare the list to the names of those who actually cast absentee ballots."

This sounds like a movie-plot failure - it mishandles voters whose address begins with the number five?!?!?! It's hard for me to imagine what accidental software bug would cause that flaw!