Which metal are you replacing? If it's iron, that is what gave you the reinforced, and why it goes away when switching to something else.
From what I can tell it looks like he is switching to Damascus Steel from Iron which also should have Reinforced on it I'm pretty sure. I think it is just a failure to update bug on the tinker table...I have a lot of problems with my sword stats not updating properly via the tinker table upgrading.