Hi Marmelade,
In earlier versions of Cinema 4D the images showed in the, e.g., left view differently than in newer version. I guess you are not working with R10.
The attached file is changed. It should now work as expected.
If you run in the same situation, in Photoshop you can use the Image>Image Rotation>Flip Canvas Horizonta, or for a single layer only use: Edit>Transform>Flip Horizontal (if it is the background layer, it needs to be selected first (CMD-A)
Enjoy the series.
Image Left side for newer versions/releases:
https://www.amazon.com/clouddrive/share/sSMisMXV19Tke0RgeZbUAUiAv91Tyz9vqkF4YaIbSTt?ref_=cd_share_link_copy