The Assignment grader interface has a feature of popping-out the form elements. These popout button links are added by some JS in mod/assignment/amd/src/grading_panel.js
That JS assumes there will only be one label tag in the area it works on, when this is not true (as in the checklist grading form: https://moodle.org/plugins/gradingform_checklist) you get some extra popout icons in odd places. (Note a CSS workaround to hide the extra popups has just been added to the gradingform_checklist addon, so it no longer displays the issue)
I think it would be possible to narrow the selectors used in this JS by adding .first() after the .find('label') and only hit the intended label in a cross-theme manner..