Have you ever wanted to annoy yourself with a full inventory even more? No? Well,too bad! 'cause here's how you do it,not in creative,but in survival! 

How the game checks if two items can stack: 
 -They are normally stackable (swords will be "no",wool will be "yes") 
 -They have the same NBT tag(s) 
We'll be messing with the second one.
Every single time you rename an item(including changing its name back) a tag known as "RepairCost" will change.This tag determines how much level you need in order to repair or rename something.Since we renamed the item in the anvil,it now has a different "RepairCost" tag than the ones we didn't name.That's why they didn't stack.