Steps to reproduce:

1. Open attached project
2. Inspect 'Test.cs' script, notice it makes a copy of a struct and compares their integer values afterwards
3. Open and play 'Scene'
4. Read the console: The 'copied' value is not 0, but some random value
5. Press 'Stop'
6. Press 'Play' again
7. Read the console again: The 'copied' value is another random value (the value is different with each play)

Expected behaviour: The copied value and the directly read value are always equal (in this case, 0)

Notes:
1. In MonoDevelop console project the issue does not occur (project is in the attached zip)
2. If you move the DoTest() method outside the struct, for example into the monobehaviour, the problem disappears
3. If you use two different structs, one inside the class and one inside the monobehaviour, the problem disappears
4. If you use a class instead of a struct, the problem disappears

Reproduced with: 5.0.4f1, 5.1.4f1, 5.2.2p3, 5.3.0b6