Why is 国语罗马字 romanized as Gwoyeu Romatzyh in Gwoyeu Romatzyh? I mean, I understand the Gwoyeu: basic forms Guo and iu, second tone turns Vu or uV into Vw or wV (right?), hence Gwo, and third tone would turn i to e, but then the y is added because the i is syllable-initial; I understand that from a basic form of tzy an -h is added for fourth tone, giving tzyh. But what about Roma? Shouldn't it be Luoma? Luo has an initial sonorant, so the second tone form is the basic form Luo, and the same goes for ma. So how come it becomes Roma in Romatzyh?
According to David Prager Branner (林德威) in A Guide to Gwoyeu Romatzyh Tonal Spelling of Chinese it is just an ad hoc rule:
The name of the city of Rome and words derived from it are to be spelled "Roma", even though they are pronounced (and ought to be spelled) Luomaa. Hence the name of this system of Romanization is spelled Romatzyh, not *Luomaatzyh.
Yuen Ren Chao was a great linguist, and in my opinion a great man. But developing a romanization single handed is too much for anyone. Apparently, on this point he felt an attachment to Rome and its cognates.