This isn't a bug exclusive to the PTS as my wife and I have experienced this on both the PTS and the normal clients, and have been since update 3, When we trade things amongst each other or with other people.. if we are getting an item in the trade that we already have in our bags they wont automatically stack, i.e. if I had 5 Grain Solvents and she went to trade me 3 additional Solvents I would have a stack of 5 and a stack of 3 in my bags as opposed to a stack of 8, or if my bags were full then she wouldn't be able to trade me those items. Hope this helps you guys, Thanks!
Edited by Lord Stark on August 26, 2014 1:23PM Lord Stark of Winterfell - VR14 Dk - NA server - Thornblade - Eminent Gaming