When Trac "Available projects" starts as an empty page
Having to use Trac instead of our usual Drupal Project* setup for a new Drupal project, I just found out a problem which perplexed me for a moment: after following the instructions from the Trac site for a very basic setup, without SVN integration, all seems to work well, up to the point where I started the server.
# tracd --port 8000 /var/www/trac/proj1
The problem
... and went to my browser to http://www.example.com:8000/ only to receive an almost empty page, just saying "Available Projects" and nothing else. No error during trac-admin initenv. And the page was well-formed, showing it was likely not an actual bug.
Googling around the problem showed the issue to be already known, but offered no hint about the solution. What could be wrong ?