Steps to reproduce( or just watch attached mp4 file):
1. Create new project in Unity 5.4.0f2.
2. Create new canvas in hierarchy menu.
3. Inside of recently created canvas create new canvas with image.
4. Resize nested canvas (the second one).
5. Enter play mode.
6. Exit play mode.

Expected results: Second canvas size should stay the same.
Actual results: Second canvas size changes.

Reproduced with: 5.4.0f2,5.4.0f1 5.2.0f3.
Not reproduced with: 5.4.0b25, 5.4.0b23, 5.4.0b20, 5.3.5p8, 5.3.5f1.

Regression introduced in : 5.4.0f1