Hi Pavel,
Welcome to the forum, and thanks so much for your report!
Because you are in a loop and the background image is on a class, the same image is displayed every time, as there is only one class. You could alternatively add the background-image to the ID of the block (as it gets converted either way), use a style=“background-image: url(…)” attribute in your block, or alternatively insert the image as a real image and then position it absolutely.
Have a look at this report, which is basically identical:
Best regards,
timmse