dropping any item that you can store in a container being, tent, barrel, chest car..etc on the ground and moving the items from vicinity to any container you want to fill skipping the hands entirely seems to fix the stuck items issue when it does happen it needs a server reset to free the items stuck or a reset to be able to get anything out of the said container.

maybe this could help you guys create a permanent fix for the stuck items putting items in your hands then to the tent, chest, barrel ..etc will cause the items to become stuck in that container cars as well.