Stacks of items can no longer be renamed in anvils. When you attempt to place a stack of items into the anvil input slot and edit the name in the bar at the top of the anvil GUI, then a single renamed item is seen in the output, vs the usual entire renamed stack. When I attempt to click this item, it disappears and one item is lost from the stack of items in the input slot and the player's experience level goes down according to the cost listed prior. However, no items are lost, as when you take the remaining items back from the input slot the item is replaced. Relogging will set the player's experience bar back to its previous value. Because of this, you can only rename items individually, one at a time. It was very costly for me to finish my hopper item filters. One level per item renamed.