If one starts to add a comment to an issue, and the window is narrower than the minimum screen width (see issue JIRA-21115), then the text entry box for the comment is the minimum screen width. But the box cannot be scrolled – the horizontal scroll bar applies to the body of the issue, but not the frame containing the comment entry box.

(This seems to be another version of "somebody is being way too clever with screen manipulation". Can't we go back to the previous screen layout which worked simply and easily and like every other web page in the universe?)