Hmm... maybe something like Zend/Turk is caching a compiled version of LocalSettings.php -- but would the web server exhibit the behavior we're seeing above if LocalSettings.php was changed I wonder?
FYI, I set:
php_value zend_optimizer.optimization_level 0
In our .htaccess file and so far haven't been able to reproduce the problem.
Any tips for using Zend Optimizer with MediaWiki that might avoid the symptoms I described?
Thanks, Ray