I created a new Picklist, I added a new item in the picklist without modifying the item that is created when the Picklist is created (NewItem...).
I added a second item (third if we count the one that was automatically created) and clicked the save button.
After I realized I didn't modify the automatically created NewItem, I deleted it. Now, I cannot edit or delete this picklist. If I click on it in the list of Picklists, I get the "loading" animation, and it comes back to the same screen. That Picklist can't be open anymore, therefore cannot be deleted nor edited...