Hello!
Not a bug, just a border missing at the popup-button "More Smileys", as I believe...
In jquery.sceditor.css it was border-left: none;
I added border-left: 1px solid #bbb;
.sceditor-more {
cursor: pointer;
padding: 0 3px !important;
margin: 2px 0 0 !important;
border-radius: 3px;
box-shadow: 0 2px 5px rgba(0,0,0,0.05) inset;
background: #fff;
border-top: 1px solid #ccc;
border-left: 1px solid #bbb;
border-right: 1px solid #bbb;
border-bottom: 1px solid #aaa;
color: #444;
}