Can anybody help me diagnose this. I've searched forums and bugzilla and couldn't find solution.

In standard Zimbra account external one was added i Settings->Accounts. When creating new mail in web client there is dropdown with accounts. After selecting external one and hitting send mail is sent with internal address in From field (visible in /var/log/zimbra.log) not external address, which is wrong and not acceptable.

Server was upgraded from 7.2.0_GA_2669 to 8.0.0.GA.5434. Is there any setting responsible for this behavior? Has anything changed during upgrade?
Can anybody point me what may be wrong or where to look, or at least debug it, please?

Thank you in advance