Ghastly Widow immune to Irritate bug?

Ghastly Widow, the spider boss in Cradle of Decay, seems to have some very weird interactions with the soldier ability Irritate. I have been in there three times this past week for purist runs, and it seems impossible to pull the boss using an irritate. After hitting irritate, the ability goes on cool down, the little animation above the boss's head shows up, but the spider just turns around and walks away slowly. As far as I can tell, it ignores irritate afterwards as I was unable to grab aggro with it after not having aggro issues on any of the other three bosses in there. I was able to use Cry of Havok to grab the boss back, but never managed to with an irritate.

This bug only seemed to occur if using irritate to pull the spider boss. If you charged in, did a combo and used irritate at the end of it, I had no problem keeping the aggro on me afterwards.