Bug using 'Quote Reply' with selected text on GitHub

I selected some text:

Chose 'Quote Reply':

And this is how it showed in the textarea:

Then as soon as I type anything in the textarea, it corrects itself:

It should show correctly from the beginning.

Start by reproducing the Quote Reply flow with selected text in the GitHub issue editor, comparing the initial textarea rendering with its state after typing. The fix is done when the quoted selection displays correctly immediately, without requiring an additional keystroke.

索引モデルが issue の本文から書いたものです。