It can still leak data if attackers can get their input reflected. I.e. I send you a word, and then I get to observe a compressed and encrypted message includin

It can still leak data if attackers can get their input reflected. I.e. I send you a word, and then I get to observe a compressed and encrypted message including my word and sensitive data. If my word matches the sensitive data, the cyphertext will be smaller. Hence I can learn things about the cipgertext. That is no longer good encryption.