Exchange 2010 with ip block list providers using custom error message generates '550-5.7.1' in agentlog files

The log field 'SmtpResponse' contains '550-5.7.1' preceding the custom error message.  The Get-Agentlog cmdlet in Exchange Management Shell throws an exception on these records as below.

The standard error message contains '550 5.7.1'. The Get-Agentlog cmdlet in Exchange Management Shell is happy on these records.

The SMTP response at line 213 in file "C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\AgentLog\Agen
tLog20150406-1.LOG" isn't formatted according to RFC 2821.
Parameter name: smtpResponse
    + CategoryInfo          : InvalidArgument: (:) [Get-AgentLog], ArgumentException
    + FullyQualifiedErrorId : 78B82C6B,Microsoft.Exchange.Management.AgentLog.GetAgentLog

Is this behavior by design? I would like to use both custom error messages and the Get_Agentlog cmdlet.

Thanks in advance.