Dynamic properties are not '.' accessible when accessing external Nodes.

[willnationsdev]

Godot version:
Godot 3.1 alpha: a92e885

Issue description:
When using _get, _set, and _get_property_list to expose a property dynamically, I have found that it functions inconsistently.

• Works
  • Test scene 3) A node exposes its own dynamic property and then prints said property using self.<property>.
  • Test scene 2) A node has an exposed Resource property with a script assigned in the Inspector. The Resource script then exposes a dynamic property. The Node prints the resource variable's dynamic property.
• Doesn't work
  • Test scene 1) The exact same code from scene 3 is used (without the print statement), but it's placed on a child node. The parent node then attempts to get the child and print the dynamic property.

I am unable to identify the reason that this occurs, so I've concluded that it is likely a bug of some kind.

Note that using .set(<property>, <value>) and .get(<property>) still works, but not using dot notation.

Minimal reproduction project:
test_dynamic_properties.zip

[willnationsdev]

cc @xDGameStudios (might be interested in following this)

[KoBeWi]

Still valid in 3.2.3 rc3
The project freezes/crashes in 6831da6 (there's a chance this is resolved on master though)