Can Reproduce BindingExpression path error: ... property not found ... On DropDownButton

[steevcoco]

I have a simple test case on GitHub:

https://github.com/steevcoco/MahAppsTests

It's a WPF XAML App. It uses a DropDownButton in a DataTemplate. The template does not set the ItemTemplateSelector, ItemStringFormat, or other properties; yet the XAML throws abundant Binding traces during execution:

BindingExpression path error: 'ItemTemplateSelector' property not found on 'object' ''ContentPresenter' (Name='')'. BindingExpression:Path=ItemTemplateSelector; DataItem='ContentPresenter' (Name=''); target element is 'DropDownButton' (Name='AccentBorderWithPopUpDropDownButton'); target property is 'NoTarget' (type 'Object')

The template does set Items in the DropDownButton ... And in the MahApps Style, there are triggers that check if the TemplatedParent ContentTemplateSelector is null and ItemTemplateSelector is not; and if so it sets the ContentTemplateSelector on the PART_ButtonContent ContentControl to the TemplatedParent ItemTemplateSelector. Perhaps the Items trigger the binding ... But I do not exactly know where the problem is. (My XAML does not set the template selectors or string format.)