Durston disc cutter

[trialuser]

Hi, not sure if this is the correct sub forum, but here goes.
I have just bought the above which arrived yesterday, thanks.
Whilst checking it over today I notice that the smallest (3mm) punch has an unusual ridged face.
This seems wrong to me, and indeed all the other punches have a machined smooth face.
Before I ask for a replacement, has anyone else here got one they could check for me please.
As it is, it would destroy the disk it was meant to be punching out.
Cookson or Durston if you're watching, is this faulty?
Thanks
Piccy attached, excuse the quality, it was iphone through microscope