MonstaMunch: I realized that was what you meant just after my post and made a ninja edit. See above ;)
Psyringe: Ah, okay. So there _are_ leap days (or months?) in the Calendar to keep it in sync, but in rural areas like the one you're in right now, only the monks understand the concepts behind it, and the villagers trust them to get it right, so they probably see no need to understand the concepts by themselves.
Edit: And yeah, religion _was_ a major source of education here in Europe too. Somehow this seems to have changed now though ... ;)
I know this might seem like an ignorant or racist thing to say, but: I genuinely don't think they even consider it. Literacy nationwide is at around 40%, and it's far lower here. I don't think they swing a bucket of water upside down and wonder why it doesn't spill out, they just notice that it doesn't spill and just keep on swinging it. All the educated people were killed during the genocide, so until recently there weren't many people you could ask if you had questions about such things.
With regards to how lunar calenders are calculated, it varies from country to country. I'll ask someone how it's calculated here when I get back to Phnom Penh.