System: Windows 10 Pro ( GTX 750 Ti )
Blender Version: 2.80 master, 2019-04-16, edc1b0167518
If I disable an object's selection in Outliner I can still transform it with another object if proportional editing is on and this object is in reach.
I discovered it on an (expectedly) locked reference image plane but you can easily reproduce it with disabling selection for the camera or light in the default scene and moving the cube with a big enough proportional edit radius.
I just tested and this behavior was present in 2.7x too.
I really hope this is not a misconception on my end - I think that disabling selection should not make this possible - otherwise how can I really lock something? (like a reference image)