To reproduce:
1. Open 1.unity scene
2. Parent Cube(2) gameObject under Cube game object
Expected result: it's parented and the scales adjust, so the object is the same in the scene
Actual result: It's scales are change, so that the child does not change from world perspective.

Note: Attached Actual/Expected result PNGs and a repro video.

Workaround: Rotate both objects to identical rotations, parent the objects, rerotate the objects to what they were before the operation

Reproduced in:
Version 5.2.4f1, 5.3.2p4, 5.4.0a6, 5.4.0b6