To reproduce:
- Create a new project
- Create a cube
- Select the cube object and go to 'Add Tag' in Inspector
- Create 2 new tags
- Apply one of the tags to the object
- Go to Inspector > Add Tag..
- Remove one of tags that you created by typing '1' in the Size parameter
- Select Cube in Hierarchy View and observe it says 'Undefined' under Tag in Inspector
- Duplicate the Cube and observe that the new cube now has the previous tag name applied.
- Select the new cube and go to "Add Tag..."
- Observe that the old tags have been recreated

Expected results: When removing tags from Tag Manager - I would not expect them to be recreated when duplicating the object.