Ok, I've had a look at them.
It turns out these were special titanium cloaks, sleeves and leggings - sold in the Castle Forecourt, from what I can see (that's the only other place I could find them).
The NPC selling them had unfortunately been set up wrong so that they sold titanium armour which ages just like any other armour but is non-repairable - they were using the template used to make crafted titanium armour.
I have fixed this NPC now so no more titanium armour bought should have this problem.