Hi there,
Ok, when you copy a block from one place to another it will carry over the blocks unique ID which is where the blocks front end styles get saved.
So, if you copied the block to your sidebar and then removed the background image, it would affect the original block you copied.
To fix that:
edit your above footer block element.
Select the parent container block, and from the block toolbar select Duplicate.
Then delete the original container.
This will regenerate the unique ID for that container and it should fix the CSS issue.