To my horror, I realised that the book I returned to National Library is belonged to Temasek Polytechnic. Not it explains why there isn't a NLB sticker at the spine of the book (Yes, I've been wondering) and why the 'Returned' wasn't lit up when I dropped the book (And yes, I actually poked my fingers in to make sure the book is not stuck but it still didn't light up.)

Oh my gracious.