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:

1. Spawn a parrot
2. Tame it by feeding it seeds
3. 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.