Reproduction steps:
1. Open the attached project "UIBug.zip";
2. Open the Test scene;
3. Press play;

Expected results: there should be a Canvas with another canvas as a child, created on a runtime and a panel inside, that fits the screen size.
Actual results: the child canvas ignores the anchoring set from the script.

Reproduced on: 2017.2.0a1, 2017.2.0b11, 2017.2.0f1, 2017.3.0b1.
Not reproduced on: 5.6.2p3, 2017.1.0f3, 2017.1.1p3.
Regression firstly introduced on: 2017.2.0a1.

Reproducible both on: Windows and Mac OSX.

Not reproducible on 2018.1.0f1.