So to answer your end question: Neither. That your familiar attacked you is a function of game AI. There's really no lore basis for it, and if this was a PnP gaming experience, the familiar would not have done that.So the suggestion I have is to pretty much ignore it on an IC level and chalk it up to an "oops".
Well, anything that is a non-LORE artifact of the NwN game engine that's chalked up to an "oops", I consider a "bug" (or unexpected, unwanted, "feature"). If Darthirâe had lost a Soul Strand over on this, it sounds like I would have reason to ask for a reimbursement (subject to documentation limits).
Is the Darkness "attack" something that is only happens when the spell is cast, or whenever someone goes into the area of effect? In other words, if Darthirâe casts Ultravision on her panther, casts darkness in the distance, and then her panther runs into the darkness, does it then want to attack her? Or is the darkness now considered an established effect, and not an attack?If an established Darkness isn't an attack, is it any different for established fields that do damage such as wall of fire?Is this any different for fields to which the familiar is completely immune, such as Mind Blank and Fear? I seem to recall not having this problem using that combination, but perhaps I was mistaken.
You might want to test your spells and buff-ups in a hostile countryside that isn't that difficult (kabold's guarding the aloe comes to mind) and use a less dangerous companion, like a badger for example.
I have used darkness with Summon Creature IX (Mithril Golem) many times, though I have never casted on-to my summon, as per clicking the darkness cast onto it, instead I always target the ground between or next to the foes.The summon has not yet attacked me.
I appreciate Dorg's perspective, but it sure looks like a bug to me. More research is needed.