Case: Inserting a horizontal rule by typing dashes (“————“) in Libre Writer causes the line to appear, but attached to the paragraph or list item before it. No selection or conventional removal methods work (Ctrl+x or select and delete/backspace).
Creating a horizontal rule with
--------- actually creates a bottom border of the preceding document block element. While formatting the borders of the element to “none” didn’t work, using Clear Direct Formatting (Ctrl+M) removed the border.