Hm. Do you have a cache mod installed like vB Optimise, or use the datastore cache option in vB's config.php file?
I had vB Optimize (lite) installed but it was deactivated.
Don't think datastore cache is activated but to be sure here is a copy from the settings in the config file:
// ****** DATASTORE CACHE CONFIGURATION *****
// Here you can configure different methods for caching datastore items.
// vB_Datastore_Filecache - to use includes/datastore/datastore_cache.php
// vB_Datastore_APC - to use APC
// vB_Datastore_XCache - to use XCache
// vB_Datastore_Memcached - to use a Memcache server, more configuration below
// $config['Datastore']['class'] = 'vB_Datastore_Filecache';
// ******** DATASTORE PREFIX ******
// If you are using a PHP Caching system (APC, XCache, eAccelerator) with more
// than one set of forums installed on your host, you *may* need to use a prefix
// so that they do not try to use the same variable within the cache.
// This works in a similar manner to the database table prefix.
// $config['Datastore']['prefix'] = '';
// It is also necessary to specify the hostname or IP address and the port the server is listening on
/*
$config['Datastore']['class'] = 'vB_Datastore_Memcached';
$i = 0;
// First Server
$i++;
$config['Misc']['memcacheserver'][$i] = '127.0.0.1';
$config['Misc']['memcacheport'][$i] = 11211;
$config['Misc']['memcachepersistent'][$i] = true;
$config['Misc']['memcacheweight'][$i] = 1;
$config['Misc']['memcachetimeout'][$i] = 1;
$config['Misc']['memcacheretry_interval'][$i] = 15;
*/