To reproduce:
1. Create a new project and import "cubemapCopyTextureBug.unitypackage"
2. Open scene "cu"
3. Press Play
4. Check generated Cubemap in the inspector window

Actual results: The generated cubemap is upside down
Expected results: The generated cubemap should be not flipped

Reproduced with: 2017.4.34f1; 2020.1.0a11

Note: The gif is attached by the user.

Code:
{
cubemap = new Cubemap(texture[0].width, texture[0].format, false);
Graphics.CopyTexture(texture[1], 0, cubemap, 0);
Graphics.CopyTexture(texture[3], 0, cubemap, 1);
Graphics.CopyTexture(texture[5], 0, cubemap, 2);
Graphics.CopyTexture(texture[4], 0, cubemap, 3);
Graphics.CopyTexture(texture[0], 0, cubemap, 4);
Graphics.CopyTexture(texture[2], 0, cubemap, 5);
}