When casting Exorcism and there are multiple units withi the area, the spirits will always prioritise the not-spell immune ones over the spell immune ones.

1. Have 2 enemies within Exorcism range
2. Have one of them activate spell immunity (bkb, repel, blade fury, rage, whatever)
3. Cast Exorcism

Result: Every single spirit will attack the unit that is not spell immune.

Expected: Exorcism ghosts shouldn't care about spell immunity at all.