fix(labels): Do not re-use mail labels if they're removable

internal_packages/message-list/lib/message-list.cjsx

@@ -227,7 +227,7 @@ class MessageList extends React.Component
       <MailImportantIcon thread={@state.currentThread}/>
       <div style={flex: 1}>
         <span className="message-subject">{subject}</span>
-        <MailLabelSet thread={@state.currentThread} includeCurrentCategories={true} />
+        <MailLabelSet removable={true} thread={@state.currentThread} includeCurrentCategories={true} />
       </div>
       {@_renderIcons()}
     </div>

internal_packages/thread-list/stylesheets/thread-list.less

@@ -48,17 +48,6 @@
     -webkit-font-smoothing: subpixel-antialiased;
   }
 
-  // Do not show the "removable" X on mail labels within the thread list.
-  .mail-label {
-    padding: 1px 8px;
-    .inner {
-      position: inherit;
-    }
-    .x {
-      display: none;
-    }
-  }
-
   .swipe-backing {
     background-color: darken(@background-primary, 10%);
     &::after {

src/components/mail-label-set.jsx

@@ -16,6 +16,7 @@ export default class MailLabelSet extends React.Component {
   static propTypes = {
     thread: React.PropTypes.object.isRequired,
     includeCurrentCategories: React.PropTypes.bool,
+    removable: React.PropTypes.bool,
   };
 
   _onRemoveLabel(label) {
@@ -45,15 +46,22 @@ export default class MailLabelSet extends React.Component {
         if (ignoredNames.includes(label.name) || ignoredIds.includes(label.id)) {
           continue;
         }
-        if (LabelComponentCache[label.id] === undefined) {
-          LabelComponentCache[label.id] = (
+
+        if (this.props.removable) {
+          labels.push (
             <MailLabel
               label={label}
               key={label.id}
-              onRemove={()=> this._onRemoveLabel(label)}/>
-          );
+              onRemove={()=> this._onRemoveLabel(label)} />
+          )
+        } else {
+          if (LabelComponentCache[label.id] === undefined) {
+            LabelComponentCache[label.id] = (
+              <MailLabel label={label} key={label.id} />
+            );
+          }
+          labels.push(LabelComponentCache[label.id]);
         }
-        labels.push(LabelComponentCache[label.id]);
       }
     }
     return (