After having tamed a parrot with seeds, you will no longer be able to feed cookies to it in order to kill it.
Steps to reproduce:
- Spawn a parrot
- Tame it by feeding it seeds
- Try to kill it by feeding it cookies
- You will be unable to feed the parrot cookies
I can't completely tell if this is the game passively telling you "no, that's messed up" or if it's really a bug, but I'd consider it a bug since you can kill untamed parrots using cookies.