Since the change of the text area to a content editable div the input field is no longer disabled while a new comment is being sent.
The problem seems to come from trying to disable the div still using the disable property; I guess that the right way to disable a content editable div would be by setting contenteditable=false, but that would need support in the core input.scss file so it has the same appearance of an input field with the :disabled pseudo-class.
@blizzz @nextcloud/designers