[IME][Windows][Chrome] Turning bold on/off during composition breaks it

[f1ames]

Is this a bug report or feature request? (choose one)

🐞 Bug report

💻 Version of CKEditor

Tested on v1.0.0-beta.2.

📋 Steps to reproduce

Extracted from ckeditor/ckeditor5-engine#1355 (comment).

1. Open the article sample.
2. Put the caret at the end of the Paragraph.
3. Press Ctrl + B.
4. Start the composition (Hiragana) and type something.
5. Press Ctrl + B.

✅ Expected result

Well, not sure what should exactly happen. On native contenteditable the composition is just continued (as one part), however if you start switching composed characters (Arrow up or Arrow down) the whole composition becomes bolded. It might be hard to mimic such behaviour.

Maybe we should just disallow turning bold off during composition? Not sure how it will affect usability for the users which create content mainly by composing.

❎ Actual result

Composition is broken, continuing typing after second Ctrl + B press reinsert whole composed part (so it is duplicated) - the good news is composition still works so you can end it and delete duplicated part.

📃 Other details that might be useful

Only on Chrome on Windows it is possible to turn off styling (e.g. Bold) during composition.

[Mgsy]

I can't reproduce it anymore.