This is a thing i've been noticing since patch 1.17a. While trading the pointer is occasionaly moving to accept button when the other person adds an item to trade. I assume its a bug because only happens sometimes and didn't happen before 1.17a.

Platform: PC
ISP: BrTurbo
Type of Internet Connection: ADSL
Internet Connection Speed: 2MB
Date & Time: 05/16/2011 11PM
Frequency: sometimes
Character Name: Lienn Deleene
Race: Miqo'te soS F
World: Istory
Class/Skill Rank: -
Physical Level: 50
Area and Coordinates: -
Party or Solo: -
NPC Name: -
Monster Name: -
In-Game Time: -
Steps:
1: Start a trade
2: Have the other person to add an item for trade. Your pointer, who is at first slot (assuming you didn't move it), will occasionaly move to accept button.