I have this happen to me on occasion at really random times. Once I was playing as my charrie, Sagitta and I was sitting at the Stone Bridge in Fluorite. After a bit, I noticed this one wolf charrie behind me kept logging on and off, each time they'd come back on resembling Sagitta a bit more. It wasn't like they just appeared as my charrie, they kept logging on and off in front of me, changing their markings and patterns every few minutes just to make sure I didn't notice. :I
Another time (This was a while ago) I was in AI with my old charrie, Xylina, and again, some person kept logging off and on, each time a bit more similar in appearance each time. A few others noticed this, but after they said something they asked, "Are you copying AlphaEclipse's character?" She only said sorry, and then 'e' dashed out of the map.
I just don't like the fact they come near me, copy my charrie, and then pretend like they didn't do a thing. With the case of Xylina, the 'copier' literally, sat next to me and would follow me, no matter where I moved. Ugh, it's just a shame people copy peoples' charries after they probably spent some time trying to think of the coloration(s) and pattern(s).
I have had this happen more times than just these two, but I only decided to list these.