help and advanced icons are shown twice for checkboxes in forms

To verify with all branches (37, 38 and master) and both with boost and classic. Preparations Copy the attached checkboxes.php to the dirroot of the site. Invoke it in the browser ( http://your.moodle-site/checkboxes.php ). Verifications A form with FOUR checkboxes is displayed (nothing, help, required and help-required). The "nothing" checkbox has no icons at all. The "help" checkbox has a blue help (question) icon on the right. Hovering on it you see the "Help with format" text. Clicking on it you see a bubble starting with the text: "The course format determines the layout...." The "required" checkbox has a red required (exclamation) icon on the left. Hovering on it you see the "Required" tooltip. The "help-required" checkbox is the union of the 2 previous points (help + required). Shown in the same places and with the same bubbles and tooltips. The form also has a legend after the checkboxes with the text "There are required fields in this form marked !". The form also has a "Show more..." link. Click on it. Now the form has EIGHT checkboxes, the original four plus four new ones, all them starting with the text "advanced". The four new checkboxes are named: advanced, advanced-help, advanced-required and advanced-help-required. The "advanced" checkbox has a blue exclamation mark on the right. Hovering on it you see the "Advanced" tooltip. The "advanced-help" is the union of the advanced + help checkboxes. Icons shown in the same places and with the same tooltips and bubbles. The "advanced-required" is the union of the advanced + required checkboxes. Icons shown in the same places and with the same tooltips and bubbles. The "advanced-help-required" is the union of the advanced + help + required checkboxes. Icons shown in the same places and with the same tooltips and bubbles. The form now has a "Show less..." link. Clicking on it hides those four advanced fields.