aptitude update 255 exit status, no errors/warnings

["Dr. Ed Morbius" <dredmorbius@gmail.com>]

Attempting my usual aptitude update and package download today:

    aptitude update && aptitude -dy full-upgrade

... I noticed that the full-upgrade didn't run.

Checking aptitude's exit status, I found it was '255', though no errors
were displayed.

Neither strace nor '-v' options (tried multiple to 4-5) provide any more
illumination.  I'll omit strace here, but -v output is:

    # aptitude -v update; echo "Status: $?"
    .
    .
    .
    Hit http://ftp.us.debian.org unstable/non-free amd64
    Packages/DiffIndex         
    Fetched 5,406 B in 13s (407 B/s)                                                
                                
    Current status: 0 broken [+0], 77
    updates [+0], 16521 new [+0]


Trying apt-get, however, gives:

    # apt-get update
    .
    .
    .
    Hit http://ftp.us.debian.org unstable/non-free amd64 Packages/DiffIndex
    W: Failed to fetch http://ftp.debian-ports.org/debian/dists/unstable/Release  Unable to find expected entry  main/binary-amd64/Packages in Meta-index file (malformed Release file?)

    W: Failed to fetch http://ftp.debian-ports.org/debian/dists/unreleased/Release  Unable to find expected entry  main/binary-amd64/Packages in Meta-index file (malformed Release file?)

    E: Some index files failed to download, they have been ignored, or old ones used instead.

(I'd added the debian-ports archive a week or so back to try to install
a package since removed from the main archive).

Obvious short-term fix is to remove debian-ports from
/etc/apt/sources.list, but it would seem aptitude's error handling
should also be improved.

Anything else I should note before filing a bug?

-- 
Dr. Ed Morbius
Chief Scientist
Krell Power Systems Unlimited