How to reproduce:
1. Open the attached "hdrpET 2" project
2. Open the "OutdoorsScene" scene
3. Select the "Ocean" GameObject in the Hierarchy
4. In the Inspector, under the "Water Surface" Component's "Miscellaneous" section, open the "Rendering Layer Mask" dropdown
5. Observe the results

Expected results: Each layer name is written only once
Actual results: "Decal" and "Light" layers are written 8 times each

Reproducible with: 6000.0.46f1, 6000.1.0b14, 6000.2.0a8

Reproducible on: macOS Sequoia 15.3 (M1)
Not reproducible on: No other environment tested