Email messages being duplicated after last DirectAdmin update

[EdsonGomes]

Problem started after the last update a couple days ago (possibly related with Exim update, but I'm speculating).
Messages received are being duplicated at the inbox, but only in the default email account.

For example, if I have a domain mysampledomain.com in my server, with 3 email accounts:

[email protected] (DEFAULT account, auto-generated, "mysampledo" is the login)
[email protected]
[email protected]

When I send test messages to all 3 accounts from and outside email (GMail, for example), the message sent to the first email is duplicated at the inbox with some additional headers ("Return-Path", "Delivered-To" and "Received") right at the top - all the rest stays exactly the same.

Already tested in 2 different servers with the same configuration, same problem, always and only in the default account.
Already tried to remove all my personalized exim filters to see if the problem was there and, nop, same results.

Can someone point me to a solution which doesn't involve "stop using the default email account", IF possible?

Thanks in advance.