Reproduction steps:
1. Open the attached project ("MultiASMDEFBug.zip")
2. Open "AssemblyOne.asmdef" asset in Inspector window
3. Tick Use GUIDs to false, press apply
4. Open different asset in Inspector and return back to "AssemblyOne.asmdef"

Expected result: Use GUIDs is false
Actual result: Use GUIDs reverts to true

Reproducible with: 2019.4.21f1, 2020.2.5f1, 2021.1.0b7, 2021.2.0a5
Could not test with: 2018.4.32f1 (no Use GUIDs option)

Note:
- If reference is set Use GUIDs works as expected