Its like the behavior you see when you quote another poster’s post and they change it after the fact. So it captures what was there at the time. It is intentional if not by design.
I don’t know what they would do to fix this or if they would want to.
This is covered in other topics here already but right now oneboxes reflect the reality of the URL at the time the “snapshot” is taken. You can only force another “snapshot” by rebaking the post, editing it, etc.