Kword does not display Japanese text correctly. In case of a paragraph with two (or more) lines, sometimes the characters at the end of the first, or the beginning of the next line are not shown. They are there, however: if characters are deleted from the first line, the missing characters appear. Also, if the cursor is placed at the beginning of the second line, and backspace is pressed repeatedly, then the missing characters are deleted first, before the cursor goes back to the end of the first line.
After many attempts to reproduce the bug, I have found that the culprit may be the "small" characters, like the sokuon (っ, "small tsu"), or ゃ (small "ya"), ゅ (small "yu") and the ょ (small "yo") character. If they fall to the end of a line, they just disappear, along with the next character (at least for me). Changing anti-aliasing or hinting has no effect on this behavior.
In the next comment I am attaching a document. It contains two paragraphs that contain the same text, only the second has more あ ("a") characters, so that the sokuon is not at the end of the line. Feel free to experience with it. For example, if the characters in the first line are deleted until the sokuon appears at the end of the line, than 'a' (Latin alphabet) is inserted, the sokuon is pushed half into the margin; next 'a' will make it disappear entirely. Half-width katakana characters have the same effect.
The document that demonstrates this bug. I forgot to tell that I am under Gutsy, and KWord is from the official repositories.