Steps to repro:

1. Open the attached project and 'LightProbeGroupBug' scene;
2. In the Hierarchy click Create>Light>Light Probe Group to add Light Probe Group gameobject;
3. Select Directional Light gameobject in the Hierarchy;
4. Select light probe group gameobject by clicking its gizmo in the Scene view;
5. Select one of the light probes in the Scene view by left-clicking on them;
6. In the Inspector click 'Duplicate Selected' button;
7. Using Editor's transform gizmos move selected probe around the scene view.

Expected result:
The new probe should be added to the scene view and should change its transform position, while the initially selected one should preserve the same position.

Actual result:
The initially selected probe changes its transform position; the duplicated light probe is not created. See attached video.

Notes:
- Reproducible in 2018.3.0a5, 2018.2.0f2, 2018.1.0f1;
- Reproducible on Windows 10;
- Duplicating with Ctrl+D shortcut works as expected;
- The issue reproduces only when there are 2 Inspectors added to the Scene.

Consider checking out https://fogbugz.unity3d.com/f/cases/1061785/ as well.