No explanation is given for why Bizarro's costume would change during his degeneration.
When Bizarro, the clone of Superman, looks at his reflection in a mirror at Lex Luthor's lab, the "S" logo on his costume is not backward. In this series (unlike the Superfriends), Bizarro's "S" logo is forward like Superman's, although slightly crooked.
Lois: (about Bizarro) Do you think he survived?
Superman: I don't know. I've never been in a half-kiloton blast. I hope he did. He turned out to have a good heart.
Lois: Well, naturally. He came from good stock.
Bizarro: What am me?
Mercy: Bizarro, that's what you am.
Bizarro: Bizarro? That not my name!
Mercy: If the shoe fits, handsome...
Bizarro: Me am Superman! Me am hero!
Lex Luthor: Sorry, my friend, but you am toast.
Lex Luthor (Bizarro crashes through Lex's Lab ceiling and then to Mercy): That's coming out of your pay.
Bizarro: I... have... problem.
Lex Luthor: My friend, I would call that an understatement.
Superman (to Superman's clone): Excuse me. I know you're a busy guy, but I'm dying to get your autograph.
Superman: It's a date!
Lois: A date? Hmm, must be this new perfume.
Superman: Take a wrong step, Mr. Kent?