BackButtonBehavior is no longer triggered once a ContentPage contains a CollectionView and the ItemsSource has been changed

[MatthewJer]

Description

If a ContentPage contains a CollectionView whose ItemsSource property is bound to an ObservableCollection, the BackButtonBehavior is no longer triggered. If the ObservableCollection or its reference is never modified, the BackButtonBehavior works as expected. The issue can be reproduced on both iOS and Android.

Steps to Reproduce

1. Check out the example repository.
2. Start the app.
3. Tap the “Navigate to other Page” button.
4. Press the Back button.
   Expected outcome: A “Hello World” alert is displayed.
   Actual outcome: The app simply navigates back.

Note:
If the following block in NewPage1ViewModel.cs is commented out, the BackButtonBehavior is triggered correctly.
Items = new ObservableCollection<NewPage1ViewModelItem>() {//You can comment out this source code and uncomment one of the other commented-out variants. The problem persists. new NewPage1ViewModelItem(), //When all variants are commented out, the BackButtonBehavior works. new NewPage1ViewModelItem(), // new NewPage1ViewModelItem() // }; //

Link to public reproduction project repository

https://github.com/MatthewJer/TestBackButtonBehavior

Version with bug

10.0.30

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

9.0.70 SR7

Affected platforms

iOS, Android

Affected platform versions

iOS26 Android16

Did you find any workaround?

No response

Relevant log output

[kubaflo]

🧪 UI Test Created for Issue Reproduction

I've created a UI test that successfully reproduces this issue:

Test Files

• HostApp: src/Controls/tests/TestCases.HostApp/Issues/Issue33688.cs
• NUnit Test: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33688.cs

Test Scenario

The test accurately reproduces the bug scenario from the original report:

1. Navigate to a page with BackButtonBehavior.Command bound to a ViewModel property
2. The page contains a CollectionView with bound ItemsSource
3. Tap a button that sets ItemsSource to a new ObservableCollection (this triggers the bug)
4. Press the back button
5. Expected: BackButtonBehavior.Command should execute
6. Actual (without fix): Command is not executed

Fix Validation

The fix from PR #33204 (GetEffectiveBackButtonBehavior) resolves this issue:

• ❌ Before fix: Test fails - "Waiting for back button..." (command not executed)
• ✅

Key Reproduction Requirements

• BackButtonBehavior.Command must be bound (not set directly)
• ItemsSource must be changed after the page is displayed
• Setting ItemsSource to a new ObservableCollection triggers the issue

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Test created by Copilot CLI

[kubaflo]

Duplicate of #33139