Back in the Ministry the day after Draco's rather eventful birthday, Hermione was surprised to see Rabastan. He didn't speak a single word to her all day. Didn't even look in her direction. His attention was focused solely on his work. Based on the incessant scratch of his quill for hours, she assumed he was writing up his official notes and report for an interrogation he conducted the previous day. It would certainly explain his absence the day before after his strange offer.