This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.
Sorry for the inconvenience if the bug really should have been left as Available.
@OP I'm not able to repro the issue. I tried both GMail and a plain contenteditable. I don't have access to document or screenshots you posted in comment #0, but here's a screencast of it working for me. Perhaps the issue has been fixed? Could you let me know if it still repros for you?