The Enter key that submits your form while a Japanese user is still typing

Here's the whole lesson up front, so you can leave after one paragraph if you want:

If your text field submits on Enter, it almost certainly submits on the Enter a Japanese, Chinese, or Korean user presses to confirm a word. That Enter isn't "send." It's "yes, that kanji." Your handler can't tell the difference unless you check one flag, and your English test suite will pass green forever while this ships. The flag is event.isComposing.

That's it. The rest is why it happens, why CI is blind to it, and a free way to pin it so it doesn't crawl back.

What actually happens

Japanese, Chinese, and Korean don't map one key to one character. You type a phonetic guess, the IME shows candidates, and you press Enter (or Space, then Enter) to pick one. That confirming Enter fires a keydown with key: "Enter", same as any other. If your submit handler only looks at key, it fires. The user was mid-word. Their first attempt is gone.