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. This causes a poor display due to padding added by user agent stylesheets to <ul> elements. With this particular HTML customization, I think we'd want to prevent TinyMCE from doing a HTML cleanup. However, there are probably other HTML customizations where we want to keep that cleanup.