Wrong og:image used for homepage

I have a “latest-post” homepage and in the “Social” tab I have always set the URL of my custom logo to show for the homepage. I have the same image/URL in the homepage settings and in the standard settings both, and it has always been all right.
Yesterday I noticed by chance that the og: image of the home page is no longer the one that I have set, but one taken from a post (probably the last one, at least the last of a certain section). I don’t know when this issue started.
I don’t use Facebook, I have seen this issue from the Firefox page of visited pages, i.e. the one you see when a new tab is opened, and then checked my homepage source page, where actually at the og:image there is the URL to the featured image of that post.

P.S.: the default homepage og:image that should be there is a .png custom logo of 178 x 153.