There seems to be undocumented requirements for romanizations of city names. Consider a Japanese city like 船橋市。 The official romanization (訓令式 / ISO 3602) would be "funabasi". This is how many people type the name with an IME. However, this is input is rejected, while "funabashi" is accepted. I'm not sure of a good solution. It may be a good idea to state the requirements somewhere
https://en.m.wikipedia.org/wiki/Hepburn_romanization
It’s no surprise to me a romanization method aimed at english speakers is used for romanizing an internet input field.