To reproduce:

1. Open the project, attached by user (CoroutineBug.zip)
2. Open "scene" scene if not open
3. Press Play
4. Observe text fade in and fade out
5. Press Bug button in the game
6. Observe text stop fading

Expected: coroutine works without stopping if new game object was created at runtime, added as a child to another game object and any UI component was added to to the new game object
Actual: creating a new game object at runtime, adding it as a child to another game object and adding any UI component to the new game object stops coroutine

Reproduced in 5.5.2p4, 5.5.3p1, 5.6.0f3, 5.6.0p2, 2017.1.0b2
Did not reproduce in 5.5.0f3, 5.5.1f1, 5.5.2f1, 5.5.2p1
Regression introduced in 5.5.2p4

Fixed in 2017.1.0b8