How to reproduce:
1. Open the user's attached "addressables-experiments" project
2. In the Project window select the "Packed Assets" Asset found in the "Assets/AddressableAssetsData/AssetGroupTemplates" folder
3. In the Inspector change the Build Path and Load Path options to "BuildTarget"
4. Save the project (File->Save Project)
5. Close and re-open the project
6. Select the "Packed Assets" again and look at the Inspector

Expected results: The Build Path and Load Path changes are saved to "BuildTarget"
Actual results: The Build Path and Load Path changes were not saved and reverted back to "<custom>"

Reproducible with: 1.3.3, 1.16.7 (2018.4.29f1, 2019.4.15f1, 2020.1.14f1, 2020.2.0b11, 2021.1.0a6)
Not reproducible with: 1.2.4 (2018.4.29f1, 2019.4.15f1, 2020.1.14f1, 2020.2.0b11, 2021.1.0a6)

Notes:
- Changing any other option with the Build Path or Load Path option and saving the project will save the path options after restarting the Editor