Basically it's to do with how market data gets synced between clients and servers.
1) Once you see a market quote, it's yours. If two people dock at once and see 100t available, then they can both buy that 100t.
2) If there's 1000t available and two people buy 100t each, then eventually the market servers will sync up and there will be 800t available. No extra cargo is created.
3) Supply, unlike demand, can't go negative. So if there is only 100t available and two people buy it, an "extra" 100t of cargo is created. If ten people buy it, an extra 900t of cargo is created.
4) This allows a lot more cargo to go to the CG than should be possible - on paper, the initial stockpile and regeneration rate should make it impossible to finish the Colonia CG before Wednesday without a lot of transport from the bubble. In practice, it'll probably be done by the end of the weekend.
If you do this on the demand side, and 10 people sell 100t to a 100t demand, you end up with a demand of -900t on the servers after everything syncs up. That displays as zero on the client, but it'll have to get through than -900t on the server at the usual regeneration rate before it goes above zero on the client.
Supply can't do this, it won't go below zero and need to catch up, so you're guaranteed to get the ten minute regen showing up (at Rock, in the current BGS state, I think about 100-150t?) and an unlimited number of people can buy and copy it.
On the one hand, this is probably a bug. On the other hand, if they fix it, then the total supply regeneration across Colonia for the CG goods would be one T-9 trip per participant per day, and the issue from the original post would be even more substantial, which would be even less fun. So the fix can't just be to allow supply levels to go negative in the background.
