I have noticed a number of problems when dealing with the games drag and drop UI:
1.) The game doesn't always register when you want to drag an item in the inventory screen. Often I will have to attempt to click-and-hold to drag items two or three times in a row to finally get the game to recognize when I am moving the item.
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I've found that you can dbl click the item to put it a back pack that is open or in the bartering dialogue if you dbl click the item it will auto appear in the storage or trade window so you don't have to Drag n Drop something which is very annoying when the UI doesn't want to respond.
