Since the last patch I've noticed a change to the character receiving an attitude increase when giving items to a trader.

Previously:

[i]Speak to a trader with character 1 then, once in the trade window, switch to character 2 (with higher barter skill). Donating items from character 2 would increase the trader's attitude with character 2.[/i]

Now:

[i]Speak to a trader with character 1 then, once in the trade window, switch to character 2 (with higher barter skill). Donating items from character 2 now increases the trader's attitude with character 1, who is in conversation with that person.[/i]

NB: I do this as I usually speak to people with my main (char 1) or persuasion (char 3) then switch to my barter character (2) if I'm trading.

I believe the previous way was intended, if a character donates items, it is their attitude which should increase. Tried this with Tarquin and Trader Haran - I believe it will work with any other character.