Bug setting transform.rotation = Quaternion.Euler(0,180,180) is inconsistent

I have issues with disappearing sprites in a 2D space shooter that I've traced to different behaviour with assigning a rotation to point straight down. (Unity 2019.2)

In a simple test project,

Code (CSharp):

1. transform.rotation = Quaternion.Euler(0,180,180)

...results in a rotation of Euler (180,0,0) and the sprite is rotated and visible.

However, in my game, the same code results in a rotation of Euler(0,180,180) and my sprite is flipped and invisible.

This affects the underlying mechanics of transform manipulation. To date, I've been assigning transform directions using

Code (CSharp):

1. transform.up = direction

. I have had some issues with flashing sprites, disappearing for a frame, that I hadn't bothered to trace up till now as I thought it was related to hidden collisions, but my current work of orbiting objects around other objects has resulted in this discovery that transform.up = direction is inconsistent when pointing straight down. transform.up = Vector3.down on some objects results in a (0,0,180) rotation, while on others, a (0,180,180) rotation.

I have been unable to create a repo case. Simple sprites in my game in test scene work correctly, with a direct facing down being drawn (and the rotation being set to Euler(180,0,0)), even with rigidbodies and colliders attached, but the same code on my objects in game is problematic. I guess it must be something to do with instantiating and parenting and who-knows-what.

Are Unity aware of any issues? Is this a bug requiring a submission? It's not a particularly easy submission for a bug report.

Edit: I have a workaround. I test if the quarternion rotation is down, and if so, set it as down from euler instead of assigning the rotation directly.

Code (CSharp):

1.     private void Start() {
2.         bugPatchRotation = Quaternion.FromToRotation(Vector3.up, Vector3.down);
3.     }
4.  
5.     private void Update() {
6.  
7.        targetRotation = Quaternion.FromToRotation(Vector3.up, direction);
8.        if (targetRotation == bugPatchRotation) {
9.            _trans.rotation = Quaternion.Euler(0, 0, 180);
10.            print("down"+ _trans.rotation.eulerAngles);
11.        } else {
12.            _trans.rotation = targetRotation;
13.        }
14.  

Note that assigning this
_trans.rotation = Quaternion.Euler(0, 0, 180);
results in transform rotation (0,0,180), but assigning this:
_trans.rotation = Quaternion.Euler(180, 0, 0);
results in transform rotation (0,180,180).

That is, this transform behaves differently to other transforms in how it deals with 180 degree rotations.