Not necessarily bugs but TinyMCE and CKeditor do not follow the same logic FCKeditor does for Heading Tags. FCKeditor shows Heading 1 but inserts H3 and Heading 2 but inserts H4, etc... I understand the reason for this is the Site Title is H1 and the Feature Instance is H2.
I think the other two editors should act the same as FCKeditor or vice versa. I don't really have a vote for which way you go as long as it is consistent.