How to reproduce:
1. Create a new project and open it
2. In the Hierarchy Window create a new cube and observe its scale and position (Position should be set to 0,0,0 and scale to 1,1,1 by default)
3. Parent the cube to the default Directional Light
4. Undo the parenting by pressing Ctrl + Z
5. Observe the cube's scale again (Position changes to -5.960464e-08,0,0 and scale to 1,1,0.9999999)

Expected result: transform values are reset correctly when undoing parenting
Actual result: transform values change by a tiny amount when undoing parenting

Reproduced with: 2020.1.0a21, 2019.3.0f5, 2019.2.20f1, 2018.4.16f1, 2017.4.36f1