I have never seen this first hand, but this may explain the situation.
Outlook Express message appears blank and has an ATT000XX.txt or an
ATT000XX.htm attachment:
http://support.microsoft.com/?kbid=312351
And from:
http://pages.prodigy.net/michael_santovec/decode.htm
Besides the problem described in this article with temporary files, Outlook
Express may have a blank message if Internet Explorer is set at View,
Encoding to Auto-Select. If so, disable the Auto-Select in Internet Explorer
and choose instead Western European (ISO). If your program has an option to
read HTML messages in Plain Text, the HTML version of the message may appear
as an ATT0001.HTM attachment (the number may vary).

Signature
Bruce Hagen
MS-MVP Outlook Express
~IB-CA~
> Some postings I receive have their subject lines altered with what appear
> to be deleted whitespace between words, and then a tab character placed
[quoted text clipped - 9 lines]
>
> Thanks, Jeff
FJ - 30 Mar 2007 01:47 GMT
>> Some postings I receive have their subject lines altered with what
>> appear to be deleted whitespace between words, and then a tab
[quoted text clipped - 23 lines]
> version of the message may appear as an ATT0001.HTM attachment (the
> number may vary).
I've followed these steps and those in the links, and still have both the
problem mentioned in my original post. Any other ideas?
Thanks, Jeff
Michael Santovec - 31 Mar 2007 02:44 GMT
It sounds like some other program is altering the posts before OE gets
them. Are you using any newsgroup proxy such as for handling yEnc
attachments?

Signature
Mike - http://pages.prodigy.net/michael_santovec/techhelp.htm
>>> Some postings I receive have their subject lines altered with what
>>> appear to be deleted whitespace between words, and then a tab
[quoted text clipped - 29 lines]
>
> Thanks, Jeff