We found a minor bug here. If you're Ninja class and follower of the purple one, and a clan member stands on a tile next to you while fighting monsters, and the Ninja lands a cursing critical hit, it will also hit the clan member. And that was in CQ3 it happened, so shouldn't be able to attack eachother as far as we tested after it happened.
Have no idea how to send the picture from this phone, but maybe Rieko can do it?

-Sigtyr

Were you using Karate skill?
Was the other player next to you?
Did you have Surround Hit skill?
Had you previously been fighting, maybe in Arena?

If you satisfy all these criteria then in theory you could hit your buddy.
If you do not satisfy anyone of these criteria then I will need to look further.

I was not using Assassinate if that was what you were asking. And it happened when Elina and I were doing a CQ, and she was on my side when I landed a Curse Critical hit and yes, I do have SH. I had 1 arena round as Ninja, and that was a hosted ML yesterday.
Strange a Purple One being able to do that tho. Not a big deal where it happened, just if it happened another place with stronger enemies, that could gone bad pretty fast. Haha.

-Sigtyr