OpacMoreSearches is supposed to be one or more <li> elements. However, when you save it in HTML customizations, it'll add a <ul></ul> tags around the <li> elements you define. Moreover, when you look at the HTML, you notice how OpacMoreSearches injects a <div> into a <ul>: <ul class="nav" id="moresearches"> <li class="nav-item"></li> <div id="OpacMoreSearches"> <div class="default_item"> <div class="default_body"> <ul> <li><a>New content</a></li> </ul> </div> </div> </div> </ul> While a lot of places where we use HTML customizations can validly inject a <div>, this isn't one of them. We might want to add a way for HTML customizations to just inject content directly without using wrappers.