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

Expected result: IEnumerator function should not stop working until the end of it.
Actual result: IEnumerator function stops working when it reaches the first yield statement after adding a graphic component to a gameObject in a layout group.

Reproduced in: 5.6.0b8, 5.6.0f1, 5.6.1p1, 2017.1.0b1, 2017.1.0b6
Not reproduced in: 5.5.3p3, 5.6.0b7

Note: adding a graphic component to a gameObject before parenting it to a layout group does not produce the bug (see gameObject "NoBug")