found a bug. not sure what exactly is causing it, as i have yet to identify the rhyme and reason for it occurring, but sometimes the gear of prisoner (despite having the full prisoner set on) still takes durability damage on occasions, though not always. Some runs it's fine, others it's not. I'll provide more info if I figure anything else out, but for now, this is about all I know about this bug.
Viewing post in Alpha Devlog 10: Public Release, Nobles and Alchemists comments
Not a bug, in forest dungeon the theme is prisoner, prisoner gear is treated as 0 durability and wont break, but can be swapped out by enemies. In caverns it is treated as all other gear and its durability goes down. This is also the case with the maid gear in the cavern. Each area has a theme and its cursed set will be treated that way.