The BakeCamera is orientated in world space.

[bithoarder]

When the BakeCamera is initially created, it is created in world space using:
_bakeCamera.transform.SetPositionAndRotation(new Vector3(0, 0, -1000), Quaternion.identity);
this will work fine in most cases, but if the canvas is in World space and the camera attached to the cavas is not Quaternion.Identity then the BakeCamera will get the inverse rotation and see the particles from a "off" angle.

Environment

• Version 4.9.1, but the code for newer 4.x and 5.x versions looks near identical.