We have a form set-up with the form layout user-assistance-density = 'compact' and the hover over question marks work everywhere except select-many and combobox-many. This can be duplicated in the cookbook ( Form Layout | Overview | JET Developer Cookbook (oracle.com) ) with the following set-up:
User Assistance Density = 'compact'
help-hints.definition = checked
After setting the form up, the hover feature works on everything except the 'many' boxes. Am I missing something or is this a bug?

