Redmine (1.3) is down

Recently our redmine issue tracker stopped working responding with internal server error 500. The log file in /var/log/redmine/default/production.log was showing errors like this:

Status: 500 Internal Server Error
private method `split' called for nil:NilClass

After a google search, the solution found on the redmine forum: For some reason, the issue seems to be caused by a passenger security update from the debian-lts team on the libapache2-mod-passenger package, so I have to rollback:

# downgrade package
aptitude install libapache2-mod-passenger=2.2.11debian-2

# and pin it via
aptitude hold libapache2-mod-passenger
# or
apt-mark hold libapache2-mod-passenger