Known Issues: Updated August 6, 2015

A little while ago, it'd go from 0% to 30% when I equipped it with no other sources of ignore DEF, so I'm guessing either it's not really broken, or it's broken and the display is wrong.

It could easily be being calculated in the screen display without actually applying to your damage. We've seen many things like that happen. (Remember when Final Attacks would show damage on screen but not do any damage to a monster?)

Side note - If you equipped 30% Ignore without NO other sources of ignore, it SHOULD show 30%.