This is 10 years late, but for whomever is still looking to get “Ignore Actor When Moving” to work here it is:
Add the actor you want to ignore to the ignore list of the primitive component that’s doing the sweep.
In the case of the Character class, if you add the actor to the CapsuleComponent’s ignore list, the character movement component uses it to filter out actors as it sweeps the root component.
In this example, I attach a shield that blocks Pawn objects to the player. To prevent any collision issues between the player capsule that’s a Pawn object and shield, I add the shield to the ignore list before attaching it to my player’s skeleton:
Hope that helps someone!