[Bug] Trust Selh'teus not attacking

I noticed when I use Selh'teus he will not move forward into melee range once the fight as started. If the fight starts and he is over by the mages he just floats there without attacking.

However, I have managed to circumvent this by calling him first in the trust order so he will follow close behind me, and be close enough to the mob when the fight starts for him actually to attack.

I'm wondering if this is some sort of bug that can be fixed, or if the Devs originally intended him to only attack sometimes, if he starts the fight close to the mob?

Thanks!