Cannot select objects in XAML Designer when using dragablz and MahApps

Question

I am developing an application with the use of dragablz, MahApps and MaterialDesign. However, I have broken down the problem to the dragablz and MahApps extension.

I create two tab items (extract from demo code):

<controls:MetroWindow x:Class="MahMaterialDragablzMashUp.MainWindow"
                      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                      xmlns:controls="http://metro.mahapps.com/winfx/xaml/controls"
                      xmlns:dragablz="clr-namespace:Dragablz;assembly=Dragablz"
                      xmlns:mahMaterialDragablzMashUp="clr-namespace:MahMaterialDragablzMashUp"
                      xmlns:dockablz="clr-namespace:Dragablz.Dockablz;assembly=Dragablz"
                      xmlns:wpf="http://materialdesigninxaml.net/winfx/xaml/themes"                      
                      WindowTransitionsEnabled="False"
                      TextElement.Foreground="{DynamicResource MaterialDesignBody}"
                      Background="{DynamicResource MaterialDesignPaper}"                      
                      GlowBrush="{DynamicResource AccentColorBrush}"                      
                      FontFamily="{StaticResource DefaultFont}"
                      Title="Material-MahApps-Dragablz Mash Up" Height="640" Width="800">
             <dockablz:Layout>
        <dragablz:TabablzControl BorderThickness="0"
                                 Margin="0,-1,0,1">
            <dragablz:TabablzControl.InterTabController>
                <dragablz:InterTabController />
            </dragablz:TabablzControl.InterTabController>
            <TabItem Header="DIALOGS">
                <mahMaterialDragablzMashUp:Mah Margin="16" />
            </TabItem>
            <TabItem Header="MAHAPPS">
                <mahMaterialDragablzMashUp:Mah Margin="16" />
            </TabItem>                 
        </dragablz:TabablzControl>
    </dockablz:Layout>
</controls:MetroWindow>

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The code works fine, but when I try to switch to another tab in the XAML designer by clicking on it, the whole section is selected but not any single object, so I cannot click on another tab:

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The view in the designer changes when I click into the corresponding code lines in the XAML editor, but not when I click on the object in the designer. This makes simple design steps (like moving buttons around) very difficult as I cannot click and drag them. Up to now, I have tried the following:

• using Visual Studio 2013 Professional
• using Visual Studio 2015 Community
• Build the project
• restart VS and the computer

I found the following question and the provided solution by 'JFTxJ' (that empty Grid elements are causing the problem) is not working for me, as I do not have any Grid items.

Same for the answer from 'Moon Waxing' (to add the attribute Visibility="Collapsed" to the tabiItem) is not working for me.

Other StackOverflow question: Cannot click or select Control XAML design

Is this a common problem or is there any solution to it?