Using 0.69 (auto-updated to 0.70 within the game) I played within a day or so of the .70 upgrade. At one point, another player (bobi) with a much lower level came to me and told me to attack him, and I said 'no'. He then attacked me, and I told him to stop. When he did not, I attacked him back, taking about 1/2 of his hit points in a few hits before he moved away. As he was leaving the area, he was attacked by a pack of bears, and killed. The death message reported "bobi was killed by a black bear", however I at the same time got the tutorial about player killing, including the line that I was now marked with the red skull of a player killer. I had no such icon on my character.
I returned to town, and talked to Io, who made no mention of the red skull at all (only wanted to know if I wanted to go over the telepathy lessons again). I talked to one of the healers, and they said I had a bad aura and they would not heal me. Leaving that character (Rocinante) logged in, I connected with another character and verified that I did not have the red skull as viewed from that account either. I tried logging out and logging in again, but still could not be healed by any of the healers.
I mentioned this to tigertoes in IRC, and we both logged in; she looked and saw nothing out of the ordinary about my account, and yet I still could not be healed. When I logged in the following morning, healing worked fine, so I assumed it was some kind of timeout issue - Kym informed me it was not, and I should file a bug.
As a possibly separate issue, should a player be marked or considered a player killer if they do not do the final blow which kills the character? On one hand, if I bleed someone down to 5hp, I might as well have killed them, but on the other hand if I only do 5hp out of 500 and a black death finishes them off, I shouldn't be responsible for that.