I hardly ever just copy and paste for the exact reason the author talks about. Instead, I try to make sense of the solution, and if I have to, I'll hand-copy it down line-by-line to make sure I properly understand and refactor from there. I also rename variables, since often times there are so many foos and bars and bazes that it's completely unreadable by a human.

Also if I come across the problem a second time, I'll have better luck remembering what I did (as opposed to blindly copying).