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.
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