I can also confirm that the very same issue occurs to me as he describes. Also another weird issue with unraring;
Although everyting is green and unraring 100%, I discover sometimes that there was no unraring at all. Upon investigating, I discovered a part or two of the rar archive had a bad CRC that was misreported to be good by the program. Therefore, I had to manually try to repair within winrar itself, which sometimes works. I could not recognize when or how this occurs and no pattern at all, as well as the unraring to the C:\ drive.