Ran out of saltpeter, yet could still build units that required it

[Badtz Maru]

In my latest game saltpeter was only available at one place on my map. I took it and started churning out gunpowder units. After a while (not sure how many turns, but I'd had gunpowder a while when I took the saltpeter and was making my first cossacks when this happened) I got the message that the saltpeter resource had run out, and it disappeared from my map. I immediately started figuring out ways to find another source, but I realized I could still build cossacks, musketmen, and cannon. I am 95% certain I don't have another source of saltpeter in my empire, and I know I'm not trading for it.

What exactly does it mean when a strategic resource goes away? Has this happened to anyone else?

[UKScud]

Sounds like you've caught a bug there.

As far as I understood, when the resource runs out, that's it...no more new units.

I mean what would be the point of denying an enemy of their resources if the 'effect' is still available after you've captured it.

Apparantly your workers can 'discover' new pockets of resources.
Maybe that accounts for the mystery???