Steps to reproduce:
1. Create a new project.
2. Create an empty game object
3. Rotate the object 90 around the y-axis in the inspector
4. Right-click on the object and go to 3D Object > Cube to create a child cube
5. Right-click again on the parent object and create another cube
6. Select both children in the hierarchy
7. Grab the X move handle (if in Global rotation) on the gizmo in the scene view and drag
8. Check cubes position in Inspector

Expected results: Both cubes have the same transforms
Actual results: One cube will be updated on X-axis.

Note: moving cube separately on X-axis reset in the correct position.

Reproduced with: 2018.1.0b1, 2017.3.0f3, 2017.2.1p1, 2017.1.2p4, 5.6.4p4, 5.5.5p1
Not reproducible with: 5.5.4p1, 5.6.2f1, 2017.1.0b10
Regression introduced in: 5.5.4p2, 5.6.2p1, 2017.1.0f1, 2017.2.0b1