How to reproduce:
1. Create a new project and in the Hierarchy Window create an empty game object
2. Add a "Horizontal Layout Group" component to it
3. Create another empty game object as a child to the previous one
4. Click on the parent object and in the "Child controls size" field tick the "Width" setting on
5. Click on the child and observe that Its Width is now locked

Expected result: From the way the label is phrased the child would have control of Its Width but not Its Height
Actual result: The child object's Width is locked - the complete opposite of what the field label says

Reproduced in: 2019.1.0a10, 2018.3.0b12, 2018.2.17f1, 2018.1.9f2, 2017.4.16f1

Note: This label was phrased correctly in the old version (5.6 and older). Changing it back to "Control Child size" would fit the functionality better