Known Issues: Updated August 6, 2015

This is working as intended. Bosses have never been affected by status ailments.

Not true. Empress has been affected by the slow status from Kaiser before.

Zakum was affected too, despite the fact that he doesn't move. The entire purpose is to inflict a status so Cursebite triggers and does the final attack thing. Why else would Giga Slash, your 1v1 DPS bossing skill, even inflict slow if it weren't meant for bosses?

And although I haven't checked any other statuses, it's become commonplace for bosses to at least get inflicted with something, even if it's reduced. That's why Mihile has a skill that inflicts Blind, but specifically states the effect or duration or something is lessened on bosses. The entire purpose is because of that whole "do more damage and crit more to enemies under a negative status" passive work.