Area2D duplicate signal when changing CollisionPolygon2D Polygon property

[ghsoares]

Godot version:
3.1 Beta 3

OS/device including version:
Windows 10 Pro

Issue description:
I'm trying to create dynamic 2d water, with damping and dispersion physics in the water surface. The water has Area2D with CollisionPolygon2D to detect RigidBody2D collision to calculate speed and apply force in a surface vertice. But the CollisionPolygon2D has the same poygon as the body (note: the water body and surface is drawed, not using a Polygon2D), so every frame is changing. But when a body enter the water, duplicate the "splash" function, but when the Collision is not changed, the "splash" function is called once.

OBS: I already tried using _physics_process(delta) function in instead of _process(delta) function to change the polygon, but the signal output more.

Steps to reproduce:

1. Create a Area2D;
2. Create a CollisionPolygon2D as child;
3. In a script, every frame change the 'polygon' property of the CollisionPolygon2D;
4. Connect the 'body_entered' signal to the script;
5. To analyse the output, put a print function on the signal;
6. Put a RigidBody2D (or other body falling to the Area2D) on the scene;
7. Run the scene.

Minimal reproduction project:
collision duplication.zip

[spikestheraccon]

I have same issue when I use Animation Player and change polygons dynamically. At the end of animation I tried to disable collision, but signal still emit. It makes impossible do "slashes" with Area2d+CollisionPolygon2d

[KoBeWi]

Still valid in 3.2.3

[Zylann]

Similar to #19271?

[ghsoares]

@Zylann It seens that both issues is occurred by the same bug, so yes