How to reproduce:
1. Open the attached "IN-150295_PrefabSelectionProblem.zip" project
2. Open the "SampleScene"
3. In the Scene view, hold the Shift key and select one of the cubes
4. Observe the selection in Scene view
Actual result: Only one of the cubes (child of a prefab GameObject) is selected
Expected result: The prefab instance root is selected
Reproducible with: 6000.5.7f1, 6000.6.0a3, 6000.6.0b7, 6000.7.0a4
Not reproducible with: 6000.0.81f1, 6000.3.21f1, 6000.6.0a2 (64de5ee36373)
Reproducible on: macOS 26.5 (By user), Windows 11
Not reproducible on: No other environments tested