[RobertM]

Actually, to a Japanese person, the spelling "Kannaduki" makes more sense, because "Duki" (pronounced as "Zuki") is a voiced version of "Tuki" (pronounced as "Tsuki".) It's done that way because the sound "Zu" can be written two different ways in Japanese, as a voiced "Tu" (Tsu) or as a voiced "Su". Doing it this way allows a Japanese person to distinguish how the kana would be written, and also allows one to type faster, since you often end up with one less letter (but not in this case).

HOWEVER, to an English speaker with no knowledge of Japanese Romaji keyboard input, it makes no sense. This is because the phrase is pronounced as "Kan-na-zuki". So for us, I think it should be spelled "Kannazuki".