Steps to reproduce :

- create a new project
- in the Hierarchy try to make a game object a child of another and notice the blue marker doesn't appear anymore
- also try to move the game object on top of another and notice that the blue line doesn't appear anymore as well
- try to drag a game object into a folder in the Project Browser and notice the folder doesn't get highlighted

*Note :

Regression from 2018.1.
Only occurs on OSX.