Reproduction steps:
1) Load multiple scenes in the hierarchy
2) Double click the header of one scene to focus on that scene
3) Select a game object(for example "cube ") of ANOTHER scene and create empty parent
4) undo create empty parent
Actual Results:
Cube moved from its original scene to the focused scene
Tested on:
- Unity Version latest main on neutron, Operating System (WIN10|MAC)
- Latest trunk (6000.3.0a4), legacy Hierarchy
Note: when fix is done please check that it is also fixed on Hierarchy v2 (which can be Enabled on trunk in Preferences)