Discounts on vending machines

[JezaGaia]

I am wondering if it's a bug or a feature that I don't understand but I wonder why once you have a good reputation with a faction and get discounts when buying from them, some vending machines of that company will give you the discount but other not.

It's even more puzzling that it happens in the same world, in one location you get the dicsount for one company but not another but on another location it might be neither or the other way around.

It never happens with NPC vendors, just vending machines.