QAT items not displayed properly if tab is made visible after initialization

[floele-ww]

QAT items not displayed properly if tab is made visible after initialization.

Actual:

Expected:

To reproduce:
Add the following code in TestContent() constructor:

        this.Dispatcher.BeginInvoke((Action)delegate
        {
            testTabItem.Visibility = Visibility.Visible;
            this.ribbon.AddToQuickAccessToolBar(testButtonForQAT);
        }, DispatcherPriority.ApplicationIdle);

Using the following existing elements (also not working with other elements):
testTabItem: <Fluent:RibbonTabItem Header="KeyTips" x:Name="testTabItem" Visibility="Collapsed"
testButtonForQAT: <Fluent:DropDownButton Header="Dropdown (auto close on click) g" x:Name="testButtonForQAT"

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Environment

• Fluent.Ribbon Current develop branch
• Windows 10
• .NET Framework 4.6