Console throws 'EndLayoutGroup" error on importing a raw terrain file.

Steps to reproduce

1. Create a project.
2. Create a terrain.
3. Click on terrain and open terrain settings in the inspector.
4. Click on 'Export Raw' and save it.
5. Click on 'Import Raw' and select the saved raw file.
6. Observe the error in console.

Reproducible on: 2018.2.0b3, 2018.2.0b1, 2018.2.0a1
Working fine on : 2018.1.0b11, 2018.1.0f2

Environment: Occurs only on mac

Stack Trace:

EndLayoutGroup: BeginLayoutGroup must be called first.
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)