Steps to reproduce:
* Edit <h1>a<i>bc</i>d</h1>
* Enable an IME (e.g. Ibus Japanese Anthy in Hiragana mode)
* Select 'bc'
* Overwrite the text with a candidate (e.g. press 'n')
* Backspace the candidate away
* Type some new text (e.g. press 'n', 'a', Enter)
Effect:
* Chromium: the new text is unannotated in the DM, but wrapped in a new bare <i> node (without class='ve-ce-textStyleAnnotation ve-ce-italicAnnotation') in the DOM.
* Firefox: The new text is unannotated in the DM. in the DOM, it depends whether your selection was inside or outside the original <i class=...> tags:
** If it was entirely outside -- e.g. you pressed home, right, shift+(right, right, right, left) -- then the new text is unannotated in the DOM.
** Otherwise -- e.g. if you pressed home, right, right, left, shift+(right, right) -- the new text appears inside the original <i class=...> node.
If we actually apply the browser richtext ( https://gerrit.wikimedia.org/r/247800 ) that will technically resolve this issue, but it will leave us wide open to replacing semantically meaningful spans with tag-styled mush that looks confusingly similar. See also T116269 .