TokenizingTextBox Binding Layout Conflict for ItemsSource

[hawkerm]

Describe the bug

Can't set binding to the TokenizingTextBox ItemsSource in XAML directly. This seems to work in the sample app, but it's doing it from code-behind after the control has been loaded.

Steps to Reproduce

Have an ObservableCollection<string> of items in my code. Then trying to bind it directly to the TokenizingTextBox:

<controls:TokenizingTextBox ItemsSource="{x:Bind MyItems, Mode=TwoWay}"/>

(Doesn't matter if OneWay or TwoWay.)

Fails on application launch.

Expected behavior

Able to bind to ItemsSource directly in XAML. It should pre-populate any items from the backing collection, and then any edits from the user should be seen in my backing collection as well.

Environment

NuGet Package(s): build746 (latest main)

Package Version(s): 

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [x] May 2020 Update (19041)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [x] May 2020 Update (19041)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [ ] 2017 (version: )
- [x] 2019 (version: ) 
- [ ] 2019 Preview (version: )

Additional context

Child collection must not be modified during measure or arrange.
   at Windows.UI.Xaml.Controls.ItemsControl.put_ItemsSource(Object value)
   at Project.Views.MainPage.XamlBindingSetters.Set_Windows_UI_Xaml_Controls_ItemsControl_ItemsSource(ItemsControl obj, Object value, String targetNullValue)
   at Project.Views.MainPage.MainPage_obj5_Bindings.Update_MyItems(ObservableCollection`1 obj, Int32 phase)
   at Project.Views.MainPage.MainPage_obj5_Bin

I am swapping out my collection object depending on if I have values, so if I remove all initializations of my backing ObservableCollection then the app loads, but the control is disabled. Though sometimes I get:

System.Runtime.InteropServices.COMException: Error HRESULT E_FAIL has been returned from a call to a COM component.
   at Windows.UI.Xaml.FrameworkElement.MeasureOverride(Size availableSize)