does dbmail mangle the position of return-path header?

on our server running postfix "Return-Path" is always at bottom and 
missing the <> but looking on servers running postfix+dovecot as well as 
gmail it's always on top and looks like Return-Path: <[email protected]>

Return-Path: [email protected]
Content-Type: text/plain

that's ciritical in case of content-filters because the position of 
received and other headers is the classification if it's trusted or not 
and in case dbmail is the reason that would explain why it's so 
difficult to pipe a message from the inbox to spamassassin and get the 
same results as at recieve time

again:
it is a MUST that every relay places it's headers ON TOP and if it also 
adds a received-header any other headers are placed above