"FocusController has unprocessed focus events" warnings are thrown when deactivating a UIDocument during an event callback and interacting with UI Containers
How to reproduce:
1. Open the attached project "uiRepro"
2. Open the scene "BugScene" and enter Play mode (Assets/BugScene.unity)
3. In the Game view, click the button labeled "Deactivate"
4. Click anywhere inside the Game view
5. Open and inspect the Console window (Window > General > Console)
Expected result: No warnings are seen in the Console
Actual result: "FocusController has unprocessed focus events. Clearing." warning is seen in the Console
Reproducible with: 1.0.0-preview.15, 1.0.0-preview.18 (2021.1.28f1), Built-in (2021.2.4f1, 2022.1.0a16)
Could not test with: 2019.4.33f1 (No UI Toolkit Package available), 1.0.0-preview.18 (2020.3.23f1) (The type or namespace name 'UIDocument' could not be found), 1.0.0-preview.14 (2021.1.28f1) (''DefaultEditorWindowBackend' Console error)
Warning in the Console:
FocusController has unprocessed focus events. Clearing.
UnityEngine.UIElements.UIElementsRuntimeUtilityNative:UpdateRuntimePanels () (at /Users/bokken/buildslave/unity/build/Modules/UIElementsNative/UIElementsUtility.bindings.cs:26)