Unable to cast object of type 'DockXamlSample.ViewModels.UserControlItemViewModel' to type 'Dock.Model.Core.IDockable'.

[IldarKhayrutdinov]

I use own hierarchy of data models without Dock models. Binding as described #228 (comment).
Add items data to model of ItemsControl throws exception (for each item):

Unable to cast object of type 'DockXamlSample.ViewModels.UserControlItemViewModel' to type 'Dock.Model.Core.IDockable'.

   at CompiledAvaloniaXaml.XamlIlHelpers.Dock.Model.Core.IDockable,Dock.Model.IsCollapsable!Getter(Object)
   at Avalonia.Data.Core.ClrPropertyInfo.Get(Object target)
   at Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings.InpcPropertyAccessor.get_Value()
   at Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings.InpcPropertyAccessor.SendCurrentValue()

The exceptions are suppressed and the window displays normally, but causes delays. There is no error when using ListBox.
Similar to #349, but on latest master throws.

Reproduction example:
DockXamlSample.zip
or https://github.com/IldarKhayrutdinov/Dock/tree/ItemsControl-Exception

[wieslawsoltes]

What version did you use?

[IldarKhayrutdinov]

The latest master revision at issue created time 9b5a3a3.
The current master version 371b790 also reproduces.