Bug damage reduction with Harlequin crest + Aspect of Hardened bones, 40%!? instead of 45

I’ve discovered a bug with the damage reduction calculation when I use Harlequin Crest + the aspect of Hardened Bones. It doesn’t count as it should, the 2 sets give me 40% damage reduction instead of 45%. In fact, when I remove Harlequin crest the aspect of Hardened bones is taken into account, 25%.