ravshalom- Is not locking your front door also tantamount to hefker?!
less chumros & Sam2- The Shulchan Aruch is refering to sefarim from his time which were handwritten and easily ruined. Many Poskim today say its allowed because the sefer will not be runied and we have a rule that Nicha Lei L’Inish L’Aveid Mitzva B’mimona a person would like that a mitzva is done with his possesions. (Sorry for the poor phonetic spelling)