Thank you for the detailed trip report stephem.
I did the PR flight in F a couple of times from YVR to MNL and your report hit the nail on the head. I wasn't as lucky as you were with the nonstop.
Eventhough the YVR-MNL is a nonstop on one flight we had to stop in ICN for re-fueling due to strong headwinds, second time we went nonstop.
About the security in SIN, it's not because of PR or flight arriving from the Philippines. I recently arrived on SQ from Auckland and we had to go through the same procedure. I think they do "spot" checks. I read a while ago about it but can't remember where.