Incorrectly regarded as a goof:
"In 'Forwards Backwards,' it said that Lois is allergic to nuts. If that is so, how was she able to make the almond brownie?"
The brownie contained walnuts and The Krelboyne Circus (Season 1 Ep 8) preceded Forwards Backwards (Season 4 Ep 5) by thirty three months. Lois could have developed/discovered the allergy later.