Index: branches/5.2.x/core/kernel/managers/cache_manager.php
===================================================================
--- branches/5.2.x/core/kernel/managers/cache_manager.php
+++ branches/5.2.x/core/kernel/managers/cache_manager.php
@@ -800,12 +800,29 @@
 			$this->setCache($serial_name, (int)$this->getCache($serial_name) + 1);
 
 			if (!defined('IS_INSTALL') || !IS_INSTALL) {
-				// delete cached mod-rewrite urls related to given prefix and id
-				$delete_clause = isset($id) ? $prefix . ':' . $id : $prefix;
+				if ( $this->Application->isCachingType(CACHING_TYPE_MEMORY) ) {
+					$prefixes = $this->Application->getCache('cached_urls_unit_prefixes');
+				}
+				else {
+					$prefixes = $this->Application->getDBCache('cached_urls_unit_prefixes');
 
-				$sql = 'DELETE FROM ' . TABLE_PREFIX . 'CachedUrls
-						WHERE Prefixes LIKE ' . $this->Conn->qstr('%|' . $delete_clause . '|%');
-				$this->Conn->Query($sql);
+					if ( $prefixes !== false ) {
+						$prefixes = unserialize($prefixes);
+					}
+				}
+
+				if ( !$prefixes ) {
+					$prefixes = array('c', 'lang', 'theme');
+				}
+
+				if ( in_array($prefix, $prefixes) ) {
+					// delete cached mod-rewrite urls related to given prefix and id
+					$delete_clause = isset($id) ? $prefix . ':' . $id : $prefix;
+
+					$sql = 'DELETE FROM ' . TABLE_PREFIX . 'CachedUrls
+							WHERE Prefixes LIKE ' . $this->Conn->qstr('%|' . $delete_clause . '|%');
+					$this->Conn->Query($sql);
+				}
 			}
 		}
 
Index: branches/5.2.x/core/units/admin/admin_config.php
===================================================================
--- branches/5.2.x/core/units/admin/admin_config.php
+++ branches/5.2.x/core/units/admin/admin_config.php
@@ -31,6 +31,7 @@
 	'ScheduledTasks' => Array (
 		'optimize_performance' => Array ('EventName' => 'OnOptimizePerformance', 'RunSchedule' => '0 0 * * *'),
 		'purge_expired_database_cache' => Array ('EventName' => 'OnPurgeExpiredDatabaseCacheScheduledTask', 'RunSchedule' => '0 0,12 * * *'),
+		'populate_url_unit_cache' => array('EventName' => 'OnPopulateUrlUnitCacheScheduledTask', 'RunSchedule' => '0 * * * *'),
 	),
 
 	'TitlePresets' => Array (
Index: branches/5.2.x/core/units/admin/admin_events_handler.php
===================================================================
--- branches/5.2.x/core/units/admin/admin_events_handler.php
+++ branches/5.2.x/core/units/admin/admin_events_handler.php
@@ -1234,6 +1234,37 @@
 		$this->Conn->Query($sql);
 	}
 
+	/**
+	 * Populates URL unit cache
+	 *
+	 * @param kEvent $event Event.
+	 *
+	 * @return void
+	 */
+	protected function OnPopulateUrlUnitCacheScheduledTask(kEvent $event)
+	{
+		$sql = 'SELECT DISTINCT Prefixes
+				FROM ' . TABLE_PREFIX . 'CachedUrls';
+		$urls = $this->Conn->GetColIterator($sql);
+		$prefixes = array();
+
+		foreach ( $urls as $url_prefixes ) {
+			$url_prefixes = explode('|', trim($url_prefixes, '|'));
+
+			foreach ( $url_prefixes as $url_prefix ) {
+				$url_prefix = explode(':', $url_prefix);
+				$prefixes[$url_prefix[0]] = 1;
+			}
+		}
+
+		if ( $this->Application->isCachingType(CACHING_TYPE_MEMORY) ) {
+			$this->Application->setCache('cached_urls_unit_prefixes', array_keys($prefixes), 3600);
+		}
+		else {
+			$this->Application->setDBCache('cached_urls_unit_prefixes', serialize(array_keys($prefixes)), 3600);
+		}
+	}
+
 }