System Information
W10 64b

Blender Version
2.80 beta, 2.79b (and previous)

Short description of error
I have this problem long time in my rigs, so I prepared this simple scene.

Expected behaviour:

It worked well in source file, but not with linked + proxy

Exact steps for others to reproduce the error

1. Link
   cubeSphereLink.blend1 MBDownload
   collection (group) to the scene
2. Make Proxy from linked (Object > Relations > Make Proxy) - use armature
3. Change Properties ("CubeSphere") on the bone in pose mode
4. Nothing change

But if you save/load file, settings is right, but you still can not change it.