Nesting <a> in <a> isn't allowed, apparently.

css/tabs.less

@@ -62,6 +62,7 @@
       position: relative;
       margin-left: 4px;
       padding-right: 4px;
+      cursor: pointer;
       
       &:hover {
         color: @foreground;

js/fileManager.js

@@ -157,7 +157,7 @@ define([
                   c({
                     value: data,
                     file: file
-                  })
+                  });
                 }, function(err) {
                   failures.push(id);
                   c(null);

templates/tab.html

@@ -2,10 +2,10 @@
   draggable
   href="tabs/{{index}}"
   command="session:raise-tab"
-  argument={{index}}
+  argument="{{index}}"
   title="{{fileName}}"
   class="tab {{animation}}"
 >
   {{fileName}} {{#modified}}•{{/modified}}
-  <a class="close" command="session:close-tab" argument={{index}}>&times;</a>
+  <span class="close" command="session:close-tab" argument={{index}}>&times;</span>
 </a>