Is it intended that PanelContainers absolutely force their children to be exactly its size -7 pixels?

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:bust_in_silhouette: Asked By leod
:warning: Old Version Published before Godot 3 was released.

I thought PanelContainers were just meant to be a visual upgrade to Containers, as the docs say it is, but when I put a Tree or anything else inside, that child will overwrite its anchors and margins as soon as I run the game or reload the view by switching between scenes.
It will always have a margin of exactly 7 pixels from each of the PanelContainer’s edges, even if all I’m trying to change is the margin (increasing it).

The same happens with multiple children, they all just take on the exact same size and overlap each other.

Am I absolutely meant to buffer everything with an extra Container in the middle?