I've seen some users forget that they chose a different password for 1Password on their Mac than the one they chose for 1Password on their iOS device(s). This can often lead to confusion (and is why we changed this in 1Password 4 for iOS).
It's my understanding that the master password was previously tied to each iOS device or computer and was not synced, so that a user could use multiple master passwords if they desired. (I agree that this can lead to confusion.) How has this been changed in 4.x? Thanks.