Sorry but you couldn't be more wrong. In Vietnam a lot of people have the same first and last names, middle names are how they differentiate.

I've been denied entry to security/airside and marched back to the desk because my middle name appeared in my passport but wasn't printed on the boarding pass.

Always include your middle name where Vietnam is involved. You'd probably get away with it, but why risk it?

The reason for the order confusion is that Vietnamese names are written Family Name - Middle Names - Given Name. Provide them per your passport and you'll be fine.