Another round of fixes for #834

Fluent.Ribbon/Controls/InRibbonGallery.cs

@@ -969,6 +969,8 @@ private static object CoerceSelectedItem(DependencyObject d, object basevalue)
         public InRibbonGallery()
         {
             ContextMenuService.Coerce(this);
+
+            this.IsVisibleChanged += this.OnIsVisibleChanged;
         }
 
         #endregion
@@ -1142,6 +1144,13 @@ public override void OnApplyTemplate()
             this.popupResizeBorder = this.GetTemplateChild("PART_PopupResizeBorder") as FrameworkElement;
         }
 
+        private void OnIsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
+        {
+            var groupBox = UIHelper.GetParent<RibbonGroupBox>(this);
+
+            groupBox?.TryClearCacheAndResetStateAndScaleAndNotifyParentRibbonGroupsContainer();
+        }
+
         private void OnPopupPreviewMouseUp(object sender, MouseButtonEventArgs e)
         {
             // Ignore mouse up when mouse donw is on expand button

Fluent.Ribbon/Controls/RibbonGroupBox.cs

@@ -869,7 +869,12 @@ internal bool TryClearCacheAndResetStateAndScale()
             return true;
         }
 
-        internal bool TryClearCacheAndResetStateAndScaleAndNotifyParentRibbonGroupsContainer()
+        /// <summary>
+        /// Tries to clear the cache, reset the state and reset the scale.
+        /// If that succeeds the parent <see cref="RibbonGroupsContainer"/> is notified about that.
+        /// </summary>
+        /// <returns><c>true</c> if the cache was reset. Otherwise <c>false</c>.</returns>
+        public bool TryClearCacheAndResetStateAndScaleAndNotifyParentRibbonGroupsContainer()
         {
             // We should try to clear the entire cache.
             // The entire cache should only be cleared if we don't do regular measuring, but only if some event outside our own measuring code caused size changes (such as elements getting visible/invisible or being added/removed).