Steps to repro:

1. Open attached project and 't1' scene on Windows;
2. In the Hierarchy select 'Terrain' gameobject;
3. In the Inspector go to 'Paint Trees' tab;
4. In the Inspector in 'Trees' section select 'Broadleaf_Desktop' tree prototype;
5. In the Scene view with active brush visible Shift-click on Terrain with trees to erase some of them;
6. Start quickly switching between Hierarchy, Inspector and Lighting tabs.

Actual result:
Editor crashes without Bug reporter and with empty stacktrace. See attached video.
Regression introduced in Unity 2018.2.0a1.

Expected result:
Editor should not crash when switching tabs after removing trees from terrain.

Notes:
- Reproducible in 2018.2.0b1, 2018.2.0a1;
- Not reproducible in 2018.1.0f1, 2017.4.1f1;
- Also OpenRL 501 errors are thrown when painting and removing tree instances from the terrain;
- Reproducible only on Windows 10 with DirectX and GlCore and on OSX with Metal;
- The issue might not reproduce steadily, if it doesn't repro, paint and then immediately erase more trees and then switch tabs;
- The issue might be hardware related;
- Not reproducible when auto-baking is turned off;
- Not reproducible with Enlighten/Realtime GI.