Behavior

1. Visit the prototype: https://patchdemo.wmflabs.org/wikis/12cdbb1f7baf0b71e7dc733aff3da949/w/index.php/Talk:Main_Page
2. Open by the Reply Tool by clicking any [ reply ] link that appears on the page
3. Ensure you are in the Reply Tool's source mode and tools like pinging "@" and linking "🔗" are visible
4. Type Hello
5. Press ⌘ + Z (for Mac users)
6. Notice the text you typed in "Step 4." (Hello) disappears

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Actual

7. ❗️Notice the text you typed in "Step 4." (`Hello) remains in the live preview.

Expected

7. ✅The live preview simply contains your signature.

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8. Switch to the tool's Visual mode

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Actual

9. ❗️Notice the text you typed in "Step 4." (`Hello) reappears

Expected

9. ✅The tool's text input is empty

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10. Switch back to the tool's source mode

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Actual

11. ❗️Notice the text you typed in "Step 4." (Hello) reappears

Expected

11. ✅The tool's text input is empty

Screen recording: https://youtu.be/ZIVy2a5gVBo .

Environment

• OS: Big Sur (11.2)
• Browser: Chrome (Version 89.0.4389.114)
• Platform: desktop

Done

• Tool is working as described in the "Expected" behavior sections of