Singapore Airport Police are psychos about checking and stamping BPs.
I (at the hotel I was staying in), in Singapore, went to the business centre, to print out on A4 paper, that boarding pass thats accepted for a lot of bookings, with AAX, and even SQ.
But when I got to Changi Airport, guess what one of those guards told me, in half broken English, I had to back track to the check in, (this was when there was an early am dep of QFi from SIN to PER), and get one of those cardboardy type of "proper" boarding passes, like what you get at the airport check in counters in Australia.
After I got the cardboardy BP, I backtracked back to Security Check, and then the BPs were duly stamped, SECURITY CHECKED or something.
Of course, the outsourced checkin girl at the gate then tore up the cardboardy BP, keeping the larger part, and giving me back the smaller part, (tail piece).
Things might have changed since 2012 or so, but expect your BP to be checked at all stages.
No fun!