- Use Gerrit new UI (polygerrit)
- Open a change and click "Reply".
- Type foo bar.
- Select the a in bar
- Type z. The text now reads "foo bzr"
- Type Ctrl + Z, which in normal text areas is "undo"
- Observe that the change was not undone: the text is still foo bzr
In step 6, the text would again read "foo bar".
This is with the new Gerrit UI (polygerrit), the old UI (GWT based) works as expected.
You could then continue by pressing Ctrl + ⇧ + Z (or Ctrl + Y, at least in my version of Firefox) which would redo the change to produce foo bzr.
You should also be able to type a long paragraph, making many edits, and use Ctrl + Z and Ctrl + ⇧ + Z to repeatedly undo and redo, as is the case in a standard textarea.
For whatever reason this bug does not occur when making an inline comment, only when using the reply popup.