Edits to the question reload the question and make the flag dialog disappear, even when I'm typing a custom moderator message.
This is annoying. I had to type the same message three times just now because the first two attempts the flag dialog was automatically closed due to edits.
Related: Don't close the flag dialog when I'm in the middle of typing something in a textbox (this is about clicking outside the dialog, not having it disappear without user intervention).