I know just what you mean about it feeling wrong. But in this case, the guideline is very, very clear--more clear than usual, I would say. No blank line even after the running head. If I may, though, I'll offer a consolation.
Print readers see a blank line immediately and read on, but braille readers can only tell by journeying across at last half of the print page, whether that line is indeed blank or bearing text. In the case of that very short alphabetical division, when centered, it also requires a journey across half the page before the reader knows it's there. The elimination of that blank line may not be so pleasing to look at for the print reader, but I suspect it improves the reading experience in braille. The braille reader has to look at only one line past the running head, catch that division letter, and immediately see text close in, if not actually at, the left margin on the very next line.