Steps to reproduce:
1. Open attached project "931748.zip"
2. Open Task Manager and look at Unity's memory usage
3. Open "Main" scene (make sure Game View aspect ratio is 16:9)
4. Enter play mode
5. Wait for cubes to spawn and use LMB to destroy them
6. Exit play mode
7. Open Task Manager and look at Unity's memory usage
8. Repeat steps 4-8

Actual result: Editors memory usage increases after each play

Reproducible with: 5.6.2p4, 2017.1.0f3