This is weird, and I only believe it happened because each time I had a witness:
Once in WT (maybe Vestrilund?) and once in Ghost Avalon (I want to say at the Malory battle), during the past few days, I have had a phantom porter join and then leave my battle. Both times, I was playing Iridian Shadowweaver.
I say phantom because:
1) He is no one on my friend's list. 2) He is no one on my friends' friend's lists. 3) He is no one our ignore lists. 4) It happened at the very beginning of the battle both times, and the wizard immediately fled BEFORE being engaged in the battle. 5) The port in and out was accompanied by a bright flash of light.
My phantom porter only ports to me, his name is Logan, and he wears red. I would assume he is a fire wizard, but he is never around long enough for me to see.
Interesting to find out the why of this, I get them occasionally. Best as I can account, it may be someone who you unfriended when they were offline, as such you remain on their list but not them on yours. Hopefully
Altho I have had this happen to me I have never noted if they were the same person, throws me off so much I don't make note of anything. I attributed it to them having signed off or marked that spot and when they came back were drug into my fight. Mine also flee which really doesn't make my day.