PanelRenderer cannot be expanded when it is unparented from another

Steps to reproduce:

1. Create and open a new project
2. Enable Hierarchy Integration in Project Settings > UI Toolkit > UI Authoring
3. Create and open a new UXML file in UI Builder
4. Add a VisualElement save and close the UI Builder
5. Add the UXML to the Hierarchy and duplicate it
6. Parent and unparent the duplicated UXML in the Hierarchy
7. Observe the Hierarchy

Actual results: The unparented UXML cannot be expanded anymore

Expected results: The unparented UXML can be expanded

Reproducible with versions: 6000.5.5f1, 6000.6.0a6, 6000.6.0b5, 6000.7.0a3

Not reproducible with versions: 6000.6.0a5

Can’t test with versions: 6000.0.80f1, 6000.3.20f1 (No in-scene UI integration)

Tested on (OS): Windows 11 Pro (25H2)

Notes:

• When the UXML is instantiated in the Hierarchy again, it can be expanded. Nothing else works (reloading window, parenting to another GameObject) except another PanelRenderer