This means that you don't have commit rights on the target branch to merge. If you had commit rights, you'd see the merge button in the overlay.

Do you mean that it's supposed to mean that? Or that it's a known issue that this happens?

I would expect the button to be something other than green in this case, and if it is clickable, for it to show why it isn't possible to merge ("You do not have commit rights on the target branch.")

This, I understand:

... although still:

... is not so helpful.