Following!! I am having the exact same issue here, it is so frustrating.
The only trick I have found was to add a blank section with no content, and make it the lowest height possible. I am using a solid colour fixed header though so I was able to make the background that colour and it matches my Header. Basically because there is no content it kind of disappears when I view the site but it means the next section background image fits the section perfectly.
I would love to know if there is code that I can use to have Full Bleed image align at the top of the actual section and not up underneath the header.