A happy ending to the story of the confused invoicer from yesterday:

I just want to let you know that your advice yesterday got me an extra $25 for the piece I wrote. After I sent the editor an email like you suggested, he wrote back, "Oh man, I'm sorry, I really f--'ed up," and he sent me a new contract. There wasn't really an explanation but he added $25 to my fee.

All in a day's work.