Steps to repro:

1. Open Unity;
2. Open attached project and 'test' scene;
3. Select 'Terrain' gameobject in the Hierarchy view;
4. Go to TerrainSettings tab in the inspector;
5. Observe tree rendering;

Actual result:
More than 5 mesh trees are rendered, though in Max Tree Settings value '5' is set (see attached actual.png screenshot).

Expected result:
5 mesh trees should be rendered in the scene; other should be rendered as billboards.

Notes:
- Reproducible in 5.5.0b4, 5.4.2p1, 5.3.6p1;
- Reproducible on both OSX 10.11.6 and Windows 10;
- Toggling Max Mesh Trees has no effect on actively rendered trees;
- Also reproducible in standalone builds.