We use Feeds and Feeds SQL to import data to Drupal from a mysql database. The credentials of the other database are written in settings.php file, so Feeds SQL can see it. On cron run, feeds fetches data from the database and inserts it into the Drupal database.
After updating to Drupal 7.20, cron system treats the other mysql database as a Drupal database and tries to find specific Drupal tables and fails with PDOException: SQLSTATE[42S02]: Base table or view not found ...
We use the same settings on another site, with Drupal 7.19, and everything works well.
The cron system is run with curl from the webserver (cron from outside the site)
log from Drupal 7.20 cron
php 02/22/2013 - 08:00 PDOException: SQLSTATE[42S02]: Base table or view not... Anonymous (not verified)
cron 02/22/2013 - 08:00 Cron run completed. Anonymous (not verified)
job_scheduler 02/22/2013 - 08:00 Finished processing scheduled jobs (0 sec s, 1 total,... Anonymous (not verified)
backup_migrate 02/22/2013 - 08:00 Default Database backed up successfully to [database_schedule_name]... Anonymous (not verified)
log from Drupal 7.19 cron
cron 2013-02-22 07:57 Cron run completed. Anonymous (not verified)
job_scheduler 2013-02-22 07:57 Finished processing scheduled jobs (0 sec s, 2 total,... Anonymous (not verified)
backup_migrate 2013-02-22 07:57 Default Database backed up successfully to... Anonymous (not verified)
I think it is a Drupal core bug because it started after the update to Drupal 7.20