AddRelativeForce() causes unwanted turning

This is a repost of the stack overflow answer posted here: https://stackoverflow.com/questions/64945203/addrelativeforce-causes-unwanted-turning There's a bounty if you're interested.

I've create a movement script that moves a character (ship) in a topdown view. Gravity is disabled, but the rest of the settings i left mostly alone.

I'm applying a constant force in the forward or backward direction (local, so relative to the character NOT the world). This however causes some movement in other directions if the character is rotated for some reason.

Debug.Log(nameof(force) + force);

             rigidBody2D.AddRelativeForce(force);

Lets me explain with pictures.

Starting point: Starting point

Moving forward somewhat (works okay): Moving forward

Back to starting point (stopping game, starting anew) And then i manually change the rotation to -90 in the inspector. I then move forward somewhat.

moving forward with rotation

As we can see since the rotation is -90, moving forward in relative to the character (AddRelativeForce(..)) causes it to move to the right on the screen. The X position increments accordingly.

However, also the Y component changes, the character gets velocity in this direction, even though i apply no force in that direction - which we can see in the output.

How can I move my character with force without this issue?

Edit:

Here are the project files. Runs under the latest unity 2020.1.14f1. The logic mentioned here is located in MoveExecuteSystem. I use a small ECS framework: https://github.com/Leopotam/ecs

https://wetransfer.com/downloads/b86dfb27b4388b85ac4fef285d87b39520201124193329/00af66