Do you have autologon enabled?
If so, it seems the keyring is the “issue”. I remember, if you disable keyring, the password is unencrypted but you should be able to save.
While it may not be a keyring issue, and you have another working fine, it still could be. It might be worth just going through that and making sure that it's absolutely not.
If you switch to having to not having auto login by default, does the same thing occur?