Expected behavior: DR stacks between Barbarian class and the Stalwart feat chain.
Current behavior: Character sheet is reporting the bonus as only the highest of the two.
In depth: At level 14, with the Stalwart and Imp. Stalwart feats (and prereqs) on a character with the Invulnerable Rager barbarian archetype, DR is listed as 7/. DR should be listed as 17/.
This (Stalwart DR) should either be attached to the combat expertise temporary bonus or have it's own temporary bonus listed, and neither of those are present. It should also not stack with any sources of DR except those gained from class features.
Note, this has only been tested on the invulnerable rager archetype.