Export PackedScene Array does not compile

[supagu]

In Godot 3,
export(Array, NodePath) var levels;
compiles fine but
export(Array, PackedScene) var levels;

fails with an error:
Expected ')' or ',' after export hint.

(Related to #3586)

[eon-s]

Object type works?

[vnen]

I believe this hint only works with built-in types.

[supagu]

export(Array, Object) var test_levels;

shows an array which I can resize in the editor, but I can't do anything with the indicies/fields. It just shows an array of and does not let me edit them in anyway.