I noticed the second one too! The reason you got another club was because the event looks to see if you have a club in your inventory, if you don't have one, you get one. The thing is, you can equip the first club it gives you, take the box again and get another club.
You can do the same with the shield, but heres another effect, you can get 2 boss keys. Even though you won't need more then one....
You can get two keys by getting the shield first then getting the club. But while getting the club, equip the first one then take the box again and in the end you'll have two clubs, two keys, one shield. I think you can get another shield if you equip your first one...
Though its not really a bug, its just exploiting the event :p