[Remops] blocked header line /^From:/

[Bergman Remailer Admin]

In regards to Bergman remailer now in testing mode:

I'm seeing the occasional warnings in my Mixmaster error.log, Like this:

[2013-09-06 14:30:01] Notice: Blocked header line: From: Echolot Pinger
<echolot at pinger.invalid> matches /^From:/.
[2013-09-06 14:52:39] Notice: Blocked header line: From: Echolot Pinger
<echolot at pinger.invalid> matches /^From:/.
[2013-09-06 16:00:02] Notice: Blocked header line: From: Echolot Pinger
<echolot at pinger.invalid> matches /^From:/.
[2013-09-06 17:00:02] Notice: Blocked header line: From: Echolot Pinger
<echolot at snorky.mixmin.net> matches /^From:/.
[2013-09-06 17:05:01] Notice: Blocked header line: From: Echolot Pinger
<echolot at snorky.mixmin.net> matches /^From:/.
[2013-09-06 17:38:38] Notice: Blocked header line: From: Echolot Pinger
<echolot at pinger.invalid> matches /^From:/.
[2013-09-06 20:05:01] Notice: Blocked header line: From: Echolot Pinger
<echolot at snorky.mixmin.net> matches /^From:/.
[2013-09-06 20:30:03] Notice: Blocked header line: From: Echolot Pinger
<echolot at snorky.mixmin.net> matches /^From:/.

What does it mean?

Am I getting these warnings because I am delivering to these pingers
directly and not through a random hop as expected for a middleman?