This is actually strange and makes me sleep deprived

The origin code is prepared such as this:

<meta property="og:image" content="" />

(the look is available, did check!) But an entirely different image is published on facebook.

The SDK is written directly following the <body> tag.

I've the best facebook-like code.

I'd exactly the same trouble with the facebook graph api. The very first you need to know happens when somebody shared your link, facebook will crawl your website for that og:image tag. Whether it does not locate them, will choose a picture available on your website. Following the first share, facebook helps you to save that images, if you added the code following the fisrt share, it's useless. You can test it with another publish. The 2nd problem would be to add

<link href="" rel="image_src"/>

for your source code. This solved my problem. I think you'll can solve it too!