How to reproduce :

• Insert a calendar (the little one) in a page with "results on the same page" parameter checked
• In the code source, go to

  <div id="all-events-{$uniqueId}">

• inside there are events, each of them are in a list item

  <li id="event-{$uniqueId}-{substring-after(content/@id, '//')}" class="event">

• The same event appears with the same Id as many times that it appears in each month of the calendar