Now I understand. This may confuse for sure even experienced user. Because if there are many wallets around, it may happen that the user completely forgets about existing passphrase.  

notgeld

If I I put a seed phrase and supply a pass phrase, my client will generate a private key. But, the client won’t store my passphrase.

So later, if I export my private key as a seed phrase, it will be different from the one I first supplied.

bitcoin

Why seed phrases are bad?

If I I put a seed phrase and supply a pass phrase, my client will generate a private key. But, the client won’t store my passphrase. 

So later, if I export my private key as a seed phrase, it will be different from the one I first supplied.

This will confuse some people, for sure.