Have just installed fresh copy of 1.11-rc1
Email settings: SMTP with authentication. All emails are working fine and being delivered to users and agents, except this case:

• User opens a ticket by sending email to support email - piping registers ticket and send email to agent
• Agent replies to ticket - User is informed by email
• User replies to agent's reply by email - reply is registered and visible in desk's website, but agent is not informed by email. Also an "API Unexpected Data. system_emails: Unexpected data received in API request" warning is registered in System log.
  I have checked all possible options in the New message alert setting:
  

Can it be related to the new unstable release or should I search for the problem somewhere else?