First 5DMK3 repair

Hi all!

I'm just about the 5DMK3 in for repair with CPS. Issue seems that higher iso values, the image i am getting has red/purple corners. Below is an image shot with lens cap on at iso 8000. I pushed exposure up a bit, so it can be easier seen. On some images it gets visible even at iso 6400. Just before I send it in, is that supposed to happen on a 5DMK3? I would sort of understand it if it would happen on all the image. But it is more present in the corners and especially the bottom ones.

Thanks!
Stefan