- Create a new animation for an object and add a curve for Transform.Position
- If you click the white dot next to Main Camera : Position, the first option there is Remove Properties (notice the plural). Selecting this will remove all Transform.position properties as expected
- If you click on the white dot next to Position.x, the first option is called Remove Property. Selecting that will also remove all properties. SOunds to me like only the Position.x property should be removed, or that menu option should also be called Remove Properties (plural)