To reproduce:
1. Open attached Unity project "CoroutineTest.zip"
2. Open "Test" scene
3. Go into Play Mode

Expected result: "CoroutineTest" script should output a message to console every 0.2 seconds indefinitely.
Actual result: a message is comes up in the console once and then the script gets disabled.

Regression first introduced in: 5.6.0b8
Not reproduced: 5.5.3p3, 5.6.0a1, 5.6.0b1, 5.6.0b6, 5.6.0b7
Reproduced: 5.6.0b8, 5.6.0f1, 5.6.1p1, 2017.1.0b5
Note: Cannot test on 5.4 because of "GameObject has multiple Transform components! Merged into single one" error.

Note: The bug does not reproduce if Rect Transform component is added manually.
Note: Attached "Expected" and "Actual" gifs.