ambition ignore works or not?

I have tested it in the past and it definitely worked.

I was using regular attack on Chief Oblivion Guardians (PDRate = 20) and hitting up to 89.96% of my range top.
As a Hero I have 40% ignore def from Combat Mastery. If Ambition's ignore def didn't work, I could only hit up to 88%.

Of course this was at least one patch ago, perhaps more, so who knows? I'll check again if I get the chance.