'port -f clean --all all' aborts with unintelligible error

[istlota@…]

I run 'port -f clean --all all' about once a week as part of my regular routine maintenance tasks. When I ran it today, it aborted after the cleaning drush msg:

Cleaning druntime ---> Cleaning drupal5 ---> Cleaning drupal6 ---> Cleaning drupal7 ---> Cleaning drush Error: Unable to open port: invalid command name "}|̂}|͹oH͹oVcc¤´­p"

I tried twice and got the same unintelligible error each time. Running port rev-upgrade reports no broken files found.

[istlota@…]

scrollback buffer from terminal session