Bug title Checkcombox绑定有问题 #1699
Description
Describe the bug
CheckComboBox多选框使用hc:ListBoxAttach.SelectedItems绑定选择项，会报警告找不到源: RelativeSource FindAncestor, AncestorType='HandyControl.Controls.TagContainer', AncestorLevel='1'。且绑定选择的内容可以通过后端更新，通过界面修改后传递过来的值就是null的了
Steps to reproduce the bug
<hc:CheckComboBox
hc:InfoElement.ShowClearButton="True"
hc:InfoElement.Title="筛选条件"
hc:ListBoxAttach.SelectedItems="{Binding SelectConditions}"
ItemsSource="{Binding FilterConditions}"
ShowSelectAllButton="True" />
Expected behavior
No response
Screenshots
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NuGet package version
None
IDE
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Framework type
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Windows version
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Additional context
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