A compilation error label can incorrectly re-appear.
Open an editor. Enter the line "asdf;" (an invalid statement followed by a semicolon). Go up a line to force compilation, then go back to the start of the line just entered (the "a" in "asdf"). The error label shows with the message "not a statement". Now, hold shift and press end to select the entire line (the label disappears). Press delete. This is an edit, so all error labels should be gone, but the error label reappears.