Dude, are you kidding? Your English is great!
Alright, ready for this one? I got it to work with roughly the same comment as I tried before-- about 4 lines Japanese and 1 line English. How'd I get it to work? I didn't enter my email address.
Haha... WTF?
So anyone who's having trouble posting, DON'T enter your email address in the email address field. (It's kind of funny, because I usually never enter my email address in things like that. Though some blogs require it, so that's why I did.) Just put a name in the top field (お名前) and your comment in the big field at the bottom (コメント).
Give it a try, I guess, though if it's set up to not accept all-English comments then I guess that doesn't help much. :?