Well, you owe me a dollar....sort of.
I was looking at my code and noticed that I had a css style associated with some of the blank rows. When the css style wasn't assigned to them or when it was assigned, but was plain, black text, there was no problem. In all of the rows that the character appeared, however, the css style was one that was bolded and set to a different color.
I have no idea why this would make a difference, but when I took out the css style, the characters were gone. So I guess it was indirectly embedded in my code, but not in any true sense.