Guild Wars 2

So here’s the question : when does MF come into play?When you actually press to loot the contents of the chest, or at the moment the chest spawned?

I’d really love to see an answer to this, because so far, I’ve ran dungeons with my MF set in the inventory and switch it only when I loot the chests.But if the loot is determined at the time of the spawn, me bringing MF gear becomes useless.
Same goes for chests from the dragons.

So, thoughts?

I’ve heard that the chest loot isn’t affected by MF at all, can anyone shed some light on this?