Reward chests (i.e. for daily crafting quests, returned artifact sets or even looting fishes while fishing) are lacking a crucial element: A "close" button that allows you to close the loot window again once you've taken a look inside.
If the prize is quite extensive and excels the amount of empty slots in your bags, you have a problem: You cannot pick up the complete loot and so close the window. It remains open until any item is taken.
If that happens in the middle of nowhere, far away from any vendor or mailbox, and without the possibility to create some space in your bags (i.e. if everthing in there is very valuable and cannot be just thrown away), you will have to run around for quite a while with that loot window open and hiding a good part of your screen.