If there's an input of type "checkboxes" within a multiple-instance template, the labels for the individual values are not clickable - clicking on them won't check/uncheck the boxes - even though they have a <label> tag around them. I believe that's due to this change I made to PageForms.js (then known as SemanticForms.js):
https://phabricator.wikimedia.org/rEPFM65d5517c9b65e58f58991c45fa86d04e209ce870
This code ends up adding a "for" attribute to all "label" tags within a multiple-instance template - even ones that are not supposed to have them - which messes up their behavior. So the JS code needs to be modified to only change the "for" value for labels that already have a "for" value.