I've had the same problem with some Japanese sites when filling out online forms (my ISP/Cable company comes to mind). It has to do with the coding format they use. With my NA Windows7/IE9 I haven't had any luck changing the settings to get it to work, to include changing the input IME. I've had to use my wife's laptop which is loaded with JP Windows7/IE9. It does suck, more so when it's a big named company (Square-Enix store's page does it to me all the time).
Believe it or not for the Japanese, there's issues with their own webpages even using JP Windows. My wife and I fought one site for hours because it wouldn't take the way we were entering in our address. It didn't like the number/special characters. The pop-up we'd get after hitting enter basically said "Correct the highlighted errors" and the address block would be outlined in red. No other information on what/why it was erroring, we just had to keep changing the input methods.
Sorry don't have an answer for you...just thought I'd share.
Pack your own lunch and bring nothing but Pixie Stix and Pop Rocks and get your liberty on.