I'm unsure of whether or not this is a bug or not, but it really did seem like it more than anything, if you steal wraithguard from an enemy Ghost, when you yourself are either Ghost off-class or not equipped with Ghost at all, you will only gain a 15% DR instead of a 30% DR from their wraithguard, I'll provide replication:
1) Be versus an enemy with Ghost as main class, and they have the wraithguard status.
2) Use Steal and successfully steal Wraithguard, while you do NOT have Ghost equipped.
3) You will only gain a 15% DR as if Ghost were your off class.
If this isn't a bug I can make another topic instead.