Unity 5.6.0f3. Odin 126.96.36.199.
Image of issue and project attached. Project includes Odin 188.8.131.52 already in it.
When using the ShowInInspector and ReadOnly attributes on a property that returns a field marked as SerializeField, the base property draws as ReadOnly, but the field that the property returns is editable.
Opening the project I have attached and opening the "Problem" scene you will see the issue on the gameobject that is in the hierarchy.