apache 2.2.21 - back to 2.2.20 ?

[n dhert]

Monday I did a portupgrade
apache-2.2.20                       <   needs updating (index has 2.2.21)
There was no problem during the update (and nothing special mentionned in
/usr/ports/UPDATING)
Today Tuesday afternoon I did a
# apachectl graceful
Since them, several webpages give problems
this error comes up:
warning: preg_match() [function.preg-match]: Compilation failed: internal
error: previously-checked referenced subpattern not found at offset 389 in
/usr/local/www/apache22/data/drupal-6.22/includes/database.inc on line 347.

nothing was changed to the website(s).
In the morning today everything was still OK. The # apachectl grafecul must
have loaded the new httpd (apache2.2.21) and now gives these
errors.
What can be the reason and how to solve?

Can you switch back tot a previous version of a port
How to go back from apache-2.2.21 to apache-2.2.20 ?