I was doing some small trades with a new friend through the TO (since we couldn't do it direct yet) and I noticed that if he listed 4 lots of something and I bought one, I could no longer see the other lots. If he posted a new trade offer I could see that but again buy only 1 lot. I tried waiting, refreshing the TO, refreshing the game and re-logging. I still could not see the remaining offers.
It seems once you buy one lot out of an offer that's all you can get from that offer. I could understand that there might be a rule in place to prevent players from hoarding up all of a certain items to control what is listed (which I wouldn't have a problem with) but I'd like to know for sure if this is by design.