To reproduce:
1. Open attached repro project
2. Open 'Test' scene
3. Open activity monitor
4. Clone '10 terrains' game object 5-7 times
5. Notice that memory usage increased as expected;
6. Delete all clones

Expected: memory usage will be the same as before cloning '10 terrains' game object
Actual: memory usage is the same as with 5-7 clones

or

1. Download project from here: https://oc.unity3d.com/index.php/s/o3J3MjDXJRjhn2t
2. Open 'TestScene';
3. Open Profiler (ctrl/cmd + 7) and 'Memory' tab;
4. Launch the scene;
5. Press X multiple times;
6. Observe that 'Used total' field is increasing. Also memory consumption is Activity Monitor or Task Manager is steadily increasing.

Regression between: 5.4.3f1 -> 5.4.3p2
5.5.0f1 -> 5.5.0f2
5.6.0a3 -> 5.6.0a5

Reproduced on: 5.4.4p3, 5.5.2f1, 5.6.0b10,
Not reproduced on: 5.4.3f1, 5.5.0a6, f1, 2017.1.0a1

Tested on: OSX 10.12.2