"Page Not Found" Error If Drupal In A Subdirectory?

After I save an edited node, I get a "Page Not Found" error that seems linked to taxonomy_similar.

For instance, when I edit this node:

http://lifetwo.com/production/node/5927/edit

... and save the edit, I get a "Page Not Found" page with this URL:

http://lifetwo.com/production//production/taxonomy_similar/node/5927

note the duplicated path and //. I suspect the cause of the problem is that I have the live version of Drupal in a subdirectory (/production). My settings.php reads:

$base_url = 'http://lifetwo.com/production';

I've had this configuration for months and taxonomy_similar is the only problematic module. It sounds like when taxonomy_similar swings into action after a post is saved, it's concatenating the URL improperly. But now we're at the limit of what I can do w/ PHP!

I installed the latest (non CVS) version of taxonomy_similar yesterday, but that did not change the problem.