How to reproduce:
1. Create a new project
2. Create a UI Document in the Project Window (Right Click > Create > UI Toolkit > UI Document)
3. Open the created UI Document
4. Add an element
5. Create another UI Document
6. In the new document add instances of the first Document
7. Unpack all added instances (Right Click > Unpack Instance)
8. Select an element
9. Observe the UI Builder Hierarchy

Expected result: Selects the element
Actual result: Multiple elements get selected from different documents

Reproducible with: 6000.3.0a1, 6000.3.0b7, 6000.4.0a4
Not reproducible with: 6000.2.0a6
Could not test with: 6000.0.60f1, 6000.2.0a7, 6000.2.0b2, 6000.2.8f1 (Different bug not allowing unpacking two of the same UI Documents)

Reproducible on: Windows 11 Pro (24H2)
Not reproducible on: No other environments tested

Note: There is a regression somewhere between 6000.2.0a7 to 6000.2.0b2