Fixes #1107

Changelog.md

@@ -35,6 +35,7 @@
   - [#1098](../../issues/1098) - Collapsed groupboxes are not keyboard accessible (thanks @cbra-caa)
   - [#1101](../../issues/1101) - Backstage button tooltip shows on active backstage (thanks @cbra-caa)
   - [#1103](../../issues/1103) - Backstage.IsOpen is not bindable (thanks @cbra-caa)
+  - [#1107](../../issues/1107) - Child sizes are not updated when user switches between Classic/Simplified Ribbon while Ribbon is minimized
   - [#1114](../../issues/1114) - Fix combobox can't open dropdown when the editable textbox of it has the focus (thanks @orrindeng)
   - [#1115](../../issues/1115) - Update Russian translation (thanks @Blueberryy)
   - [#1116](../../issues/1116) - Accessibility: Ribbon Display Options are read as "DropDown Button"

Fluent.Ribbon/Controls/RibbonGroupBox.cs

@@ -687,15 +687,9 @@ public bool IsSimplified
     /// </summary>
     private static void OnIsSimplifiedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
-        if (d is RibbonGroupBox ribbonGroupBox)
-        {
-            // We have to run this async in the dispatcher as the panel containing all controls is re-created
-            ribbonGroupBox.RunInDispatcherAsync(() =>
-            {
-                ribbonGroupBox.TryClearCacheAndResetStateAndScaleAndNotifyParentRibbonGroupsContainer();
-                ribbonGroupBox.updateChildSizesItemContainerGeneratorAction.QueueAction();
-            }, DispatcherPriority.Background);
-        }
+        var box = (RibbonGroupBox)d;
+        box.TryClearCacheAndResetStateAndScaleAndNotifyParentRibbonGroupsContainer();
+        box.updateChildSizesItemContainerGeneratorAction.QueueAction();
     }
 
     private static void UpdateIsSimplifiedOfUIElement(DependencyObject? element, bool isSimplified)