[Mac, TextArea] Japanese IME, caret moves to the next line when pressing Return to select a candidate.

This only happens on Mac.
Steps to reproduce:
1. Focus on a TextArea, invoke IME for Japanese.
2. Type string "tsu".
3. Press "Space", the string is converted to a Japanese characters.
4. Press "Space" again, the candicate windows is displayed.
5. Press "Return" to confirm the selection.
6. Press "Return" to commit the Japanese text.

In step 5, the selection is confirmed, but the caret moves to the next line. It should be staying at the end of the composing text.