also the act of copying sometimes generates a temp file of equal size to facilitate the copy.
if you "X"d out of the program,or if it didnt close down properly that file might not have been cleaned up..
someone pointed me to a program called space monger..it shows all the files on your pc in a graphical form.the larger the file the larger the box and subsequently its given diffent colors as well, red for big,green for small..great for finding large files that might not be named something you know and could find, like a temp file.