Email header randon(?) changes

[t.p. <[e-mail]>]

Why does the format of the messages on i-d-announce for I-Ds change
format on a seemingly random basis?

The change that bugs me is the appearance and disappearance of the space
after action and before draft, which completely upsets my filtering, and
given the deluge of e-mails that will appear later this month, that
wastes my time.

Thus
Subject: I-D ACTION:draft-lan-nvo3-qtp-01.txt
versus
Subject: I-D Action: draft-lanthaler-profile-registry-05.txt

The CAPS do not bother me, nor does the switch between

Content-Type: text/plain; charset="us-ascii"
and
Content-Type: multipart/mixed; boundary="NextPart"

but that little old space does.  And this is not new.

Any ideas?

Tom Petch