(effects all versions) The fishing rod bobber entity does not have an entity name(such as Zombie or EnderCrystal).
Steps to replicate:
1. Throw out a fishing rod bobber
2. run this command: /testfor @e[type=!Player,r=10] (make sure the bobber is in a 10 block radius and there aren't too many entities around so you can see it)
3. notice how it says "found unknown"