Actually, I found out the reason, at least I'm pretty sure. Though the jammer was never on at first, he turned it on when the missiles were close. Due to that the range gate lost track of him, and stayed where it last saw him. So when he came closer the AAR correctly registered that I'd been firing at a target that was far above 24.000m altitude according to the settings I'd inadvertently been feeding the Fan Song.
So no problem, just a user bug
