Steps to reproduce:

1. Create a new Unity Project
2. In the Hierarchy, add a UI Document GameObject
3. In the Project window, create a new UI Document (UXML) via Assets > Create > UI Toolkit > UI Document
4. Open the UXML in the UI Builder
5. Make some changes in the UI Builder (e.g. add a button) without saving
6. Enter Play Mode
7. While still in Play Mode, maximise the UI Builder window and then return it to its previous size
8. Alternatively, attempt to make edits in the UI Builder while in Play Mode
9. Observe the Console for warnings

Actual results: A warning appears in the Console: " UI was recreated and no companion MonoBehaviour found, some UI functionality may have been lost.
UnityEngine.UIElements.UIElementsRuntimeUtilityNative:UpdatePanels () (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Native/UIElementsUtility.bindings.cs:21)"

Expected results: UI Builder should not throw warnings when editing unsaved changes in Play Mode

Reproducible with versions: 6000.2.0b1

Tested on (OS): macOS 15.5 (Silicon M4), Windows 11

Notes:

•  A UI Document GameObject must be present in the Hierarchy during Play Mode
• This issue may confuse users and hinder iterative UI development workflows