Over scroll of bottom sticky headers should be fixed, and expansion of hidden stuck headers should now work

src/components/structures/RoomSubList.js

@@ -115,15 +115,21 @@ var RoomSubList = React.createClass({
         });
     },
 
+    // The header is collapsable if it is hidden or not stuck
     // The dataset elements are added in the RoomList _initAndPositionStickyHeaders method
-    isHeaderStuck: function() {
+    isCollapsableOnClick: function() {
         var stuck = this.refs.header.dataset.stuck;
-        return stuck !== undefined && (stuck === "top" || stuck === "bottom");
+        var topBottomSticky = this.refs.header.dataset.topBottomSticky;
+        if (this.state.hidden || stuck === undefined || stuck === "none") {
+            return true;
+        } else {
+            return false;
+        }
     },
 
     onClick: function(ev) {
-        if (!this.isHeaderStuck()) {
+        if (this.isCollapsableOnClick()) {
-            // The header is not stuck, so the click is to be interpreted as collapse and truncation logic
+            // The header iscCollapsable, so the click is to be interpreted as collapse and truncation logic
             var isHidden = false;
             var isTruncatable = this.props.list.length > TRUNCATE_AT;
 

src/skins/vector/css/matrix-react-sdk/views/rooms/RoomList.css

@@ -32,3 +32,8 @@ limitations under the License.
     overflow-x: hidden ! important;
     overflow-y: scroll ! important;
 }
+
+/* Make sure the scrollbar is above the sticky headers from RoomList */
+.mx_RoomList_scrollbar .gm-scrollbar.-vertical {
+    z-index: 3;
+}

src/skins/vector/css/vector-web/structures/LeftPanel.css

@@ -49,7 +49,6 @@ limitations under the License.
     flex: 1 1 0;
 
     overflow-y: auto;
-    z-index: 3;
 }
 
 .mx_LeftPanel.collapsed .mx_BottomLeftMenu {

src/skins/vector/css/vector-web/structures/RoomSubList.css

@@ -21,7 +21,7 @@ limitations under the License.
 }
 
 .mx_RoomSubList_labelContainer {
-    height: 29px;
+    height: 31px; /* mx_RoomSubList_label height including border */
     width: 235px; /* LHS Panel width */
     position: relative;
 }