My Google Apps account has an email primary@mydomain.org and an alias alias@mydomain.org. Aliases share same inbox so my KMail has one IMAP and two SMTP account one for primary and one for alias. I have created two identities which are exactly same but with two differences. Email address are different and Outgoing account has their own smtp.  When sending email If I choose alias identity and it has alias smtp in outgoing account then it gives following error

Failed to transport message. Your SMTP server does not support PLAIN. Choose a different authentication method. The server responded: 5.7.8 Username and Password not accepted. Learn more at 5.7.8 http://support.google.com/mail/bin/answer.py?answer=14257 vl1sm2292747pbc.62 - gsmtp

if I don't select an outgoing account in alias then everything works fine. My emails are sent without any errors. 

The reasons I want two identities is because I want emails sent to alias to be sent via alias smtp and primary to be sent via primary smtp account.

Reproducible: Always

Steps to Reproduce:
1. Setup primary and alias account/identities.
2. Make both identities choose their own aliases.
3. Send email using alias identity.

Actual Results:  
Emails are not sent from alias account if I choose its smtp for outgoing account in smtp. 

Expected Results:  
If I don't choose its own smtp then KMail would choose the default smtp account. Since aliases act as separate email accounts they should be able to use their own smtp accounts.