Reproduction steps:
1. Open the attached project ("case_1238181-ResourcePath.zip")
2. Open the Addressable Groups window
3. Inside the window, select 'Cubes/ReproCube.prefab' asset and inspect its address
3. Make 'Resources/Cubes/ReproCube.prefab' addressable
4. When asked to move to 'resources_moved', select yes
5. Inspect the moved asset's address

Expected result: Asset address remains 'Cubes/ReproCube'
Actual result: Asset address becomes 'ReproCube'

Reproducible with: 2018.4.22f1, 2019.3.12f1, 2020.1.0b8, 2020.2.0a10
Reproducible with package versions: 1.2.3, 1.8.3

Note:
Changing the MoveAssetsFromResources method from:
-- var newAddress = Path.GetFileNameWithoutExtension(oldPath.Substring(index + 10));
to:
++ int length = oldPath.Length - (index + 10 + Path.GetExtension(oldPath).Length);
++ var newAddress = oldPath.Substring(index + 10, length);
fixes the issue