I have enabled numbered headings but I think this should be bypassed when the heading is just a single letter (used quite a lot in alphabetical lists) as it looks quite strange. See http://en2.wikipedia.org/wiki/List_of_Latin_phrases if you have headers enabled to see what I mean.
Actually, perhaps it would be better to put a colon between the number and header. "6: F" instead of "6 F", which looks like a school class name.
Thoughts?