System Information
Operating system: Kubuntu 18.04
Graphics card: NVidia GTX1060 3GB

system-info.txt generated from blender is attached.

Recreate problem:

1. Fresh blend file
2. Add armature (single bone)
3. Add plane
4. Parent plane to armature
5. Select armature, go in pose mode
6. Hide armature (I used the eye-icon from outliner for this)
7. See mode display: it says "Object mode" now
8. Try to select the plane - won't work

Solution:

1. Unhide armature
2. Select armature, go from pose mode back to object mode
3. Hide armature again
4. Now you can select the plane

Edit:
I forgot to describe the actual problem: If the user doesn't realize, that the rig got hidden while it was in pose mode, they are trapped in a state where they cant select another object.