There are two poll books, each with a full set of names of registered voters. When a voter decides which primary he wants to vote in, his choice (or party) is recorded in that book.
In some precincts, probably not all of them, the election administrators used the DEM book, which identifies the people who voted in the DEM primary. This is a quick and reliable way (or should be) to prevent a person who voted in the DEM primary from voting the GOP runoff.
So... they used the Democratic poll book (even though it was a Republican primary) on 6/24 to prevent illegal double-voting, and then went ahead and allowed people to illegally double-vote anyway and recorded the fact that it had occurred (instead of just using the Republican poll book so that they could plausibly claim honest error and avoid creating an obvious written record)?
My brain hurts.