To reproduce:
1.Create new Unity project
2.Create a terrain in the hierarchy
3.Observe in the scene window that it is visible
4.Try to zoom out until it becomes invisible

Expected result: terrain is visible when zooming out
Actual result:terrains becomes invisible when zoomed out a bit

Reproduced on:2017.2.0b5 2017.3.0a1 2017.3.0a2
Not reproduced on: 2017.1.0f3 2017.2.0a1 2017.2.0b1 2017.2.0b3
Regression introduced in 2017.2.0b4

Notes: WINDOWS ONLY