Binding errors on raw CheckComboBox

[ChoKaPeek]

Describe the bug

With a simple CheckComboBox, two binding errors on CheckComboBoxItem's VerticalAlignment and HorizontalAlignment properties are triggered at runtime. I replicated it in an empty WPF project targeting .net Framework 4.8 and can't seem to fix it from outside.

Steps to reproduce the bug

• New WPF project (.Net Framework 4.8)
• HC version 3.3, 3.2
• Basic MainWindow.xaml:

<Window x:Class="TestCheckComboBox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:hc="clr-namespace:HandyControl.Controls;assembly=HandyControl"
        xmlns:local="clr-namespace:TestCheckComboBox"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.Resources>
            <ResourceDictionary>
                <ResourceDictionary.MergedDictionaries>
                    <ResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/SkinDefault.xaml" />
                    <ResourceDictionary Source="pack://application:,,,/HandyControl;component/Themes/Theme.xaml" />
                </ResourceDictionary.MergedDictionaries>
            </ResourceDictionary>
        </Grid.Resources>

        <hc:CheckComboBox/>
    </Grid>
</Window>

Expected behavior

No response

Screenshots

(Translation: Source can't be found)

NuGet package version

HandyControl 3.2.0

IDE

Visual Studio 2019

Framework type

.Net Framework 4.8

Windows version

October 2020 Update (19042)

Additional context

No response