I hope this is the right place to report bugs
While I am in trade mode I can split items from my inventory to the trade section. However, I can;t split items inside my own inventory. Doing that only moves the item to the new slot. It also re-consolidate any items I've split before - from my inventory and from the trade area - they all group up again and move to the new slot.
I also noticed that entering trade while I have items split in my inventory will re-consolidate those items to one stack.
