1. Currently, if you weigh 350 stones, and you drag something that weighs 100 stones from your bank onto someone attempting to do trade menu, you will get an error stating that you wouldn't be able to carry the item if the trade menu failed. In t2a, this would simply drop below you if the trade window failed.
2. Currently, if you try to trade an item that is 100 stones and the recipient weighs 350 stones, you will get an error saying that the recipient cannot carry the item. In t2a, if the trade was successful the item would drop below the recipient.
3. Currently, you cannot trade an item that was just stolen for about a minute. In t2a, you were able to trade an item right after it was stolen.
4. Currently, I believe that you cannot trade trapped pouches. In t2a, you were able to do so.
Here is the patch note from Feb 2000 stating that this was being changed:
http://update.uo.com/design_168.html
Server Publish Feb 23 2000 10:22AM CST
Trade Window Changes
Trade windows will become more secure.
* You will not be able to trade a trapped item.
* You will not be able to trade an item that was recently stolen.
* You will not be able to trade items to a player if that player cannot hold the items.
o If the items are too heavy for the player or if the items would exceed the number of items the player can carry, the trade will fail. All items in the trade window will go back into each character’s pack.
* You will not be able to pick items up while the trade window is open. However, you will still be able to rearrange items in your own pack during the trade.