(5.2.1f) Child Canvas alters its transform's anchor position when added to a parent

My project has a gameobject hierarchy like this.

Canvas Root(the one you create via right click>ui>canvas)
-Child Canvas(a game object with canvas component)
-Child Canvas
-Child Canvas
-.....

Those Child Canvases are prefabs and their anchor positions are set to both stretch/stretch but when you add them to the Canvas Root, their anchor positions are automatically altered to left/bottom. This behaviour/bug was not present in 5.1.

You can reproduce it by just making a new project and make...

(5.2.1f) Child Canvas alters its transform's anchor position when added to a parent