Here is a new one on me - I'm really annoyed (and I'm relieved I found it so soon). I had discovered that a line in one of my trees also is in another, so to shortcut the process, I decided to do a "save to another tree" for some of the folks, with the records then to be added since I know what they are. The first person I chose was the third wife, who had five children with the husband. I thought when adding that it looked like more children than I remembered her having - and when I went back to compare with the source profile, I discovered that the system had added all of her husband's children from two prior marriages (total of 12), as "her" children.
This is at best alarming - I told the system to do one thing, and it did another that is not warranted by the records. Now, I have to either add the other two wives and laboriously go in and change all the relationships of the collective children, or else remove the ones who are not children of the third wife, and try to keep it straight when adding the other two.
Bottom line, the system just created a totally wrong section of my tree - on its own - when it was supposed to only COPY what was there, not make up children this woman did not have and who are not in the profile I was copying. (Maybe this accounts for some of the duplicates spawned by the clickologists who don't actually read the product they have created?)