Go to master/calendar/export.php?theme=clean
ask for the html source
and look for `Events related to courses`.
You will find:

{{<span>
    <input name="events[exportevents]" value="courses" type="radio" id="id_events_exportevents_courses" />
    <label for="id_events_exportevents_courses">Events related to courses</label>
</span>}}
All is correct.

Now perform the same check using boost.

Go to master/calendar/export.php?theme=boost
ask for the html source
and look for `Events related to courses`.
You will find:
{{<label class="form-check-inline form-check-label  fitem  ">
    <input type="radio" name="events[exportevents]" id="id_events_exportevents_courses" value="courses" type="radio" >
    Events related to courses
</label>}}

As you can see, you can find the attribute `type` of the radio `input` tag twice.