This happened to me too, once on Friday 3/16 and on 3/17. The res showed up as not ticketed under "My Reservations" and i got a confirming email. So, I canceled them online, and they don't even show up in my canceled reservations (in contrast to one "real" reservation I canceled, which does show up there). I did get emails confirming the cancellations of these ghost reservations. There are no pending charges to my credit card, which I haven't saved in my UA account anyway.

I noticed that a chat window opened up when I hit the back button when I had gotten to the traveler info page, when pretending to make the reservation. I think that is what may have triggered it, but I'm not sure.

I'm not worried about it. Usually UA charges your credit card in a nanosecond, so if it hasn't shown up on your cc yet, you're probably in the clear.