Patch for WP Memcached Object Cache to make key generation dynamic instead of static; fixes problems with switch_to_blog()

object-cache.php.diff

--- a/wp-content/object-cache.php
+++ b/wp-content/object-cache.php
@@ -263,10 +263,18 @@ class WP_Object_Cache {
   	if ( empty($group) )
 			$group = 'default';
 
+		global $blog_id, $table_prefix;
+		$global_prefix = '';
+		$blog_prefix = '';
+		if ( function_exists( 'is_multisite' ) ) {
+			$global_prefix = ( is_multisite() || defined('CUSTOM_USER_TABLE') && defined('CUSTOM_USER_META_TABLE') ) ? '' : $table_prefix;
+			$blog_prefix = ( is_multisite() ? $blog_id : $table_prefix ) . ':';
+		}
+
 		if ( false !== array_search($group, $this->global_groups) )
-			$prefix = $this->global_prefix;
+			$prefix = $global_prefix;
 		else
-			$prefix = $this->blog_prefix;
+			$prefix = $blog_prefix;
 
 		return preg_replace('/\s+/', '', WP_CACHE_KEY_SALT . "$prefix$group:$key");
 	}
@@ -382,14 +390,6 @@ class WP_Object_Cache {
 			}
 		}
 
-		global $blog_id, $table_prefix;
-		$this->global_prefix = '';
-		$this->blog_prefix = '';
-		if ( function_exists( 'is_multisite' ) ) {
-			$this->global_prefix = ( is_multisite() || defined('CUSTOM_USER_TABLE') && defined('CUSTOM_USER_META_TABLE') ) ? '' : $table_prefix;
-			$this->blog_prefix = ( is_multisite() ? $blog_id : $table_prefix ) . ':';
-		}
-
 		$this->cache_hits =& $this->stats['get'];
 		$this->cache_misses =& $this->stats['add'];
 	}

Posted writeup to WordPress plugin forum: http://wordpress.org/support/topic/issue-with-multisite-and-use-of-switch_to_blog?replies=1#post-3541617