Index: bp-core-classes.php
--- bp-core-classes.php
+++ bp-core-classes.php
@@ -1331,13 +1331,17 @@
 			return false;
 		}
 
+		$retval = array();
+
 		// get cache for single user only
 		// @todo Why only single user?
 		if ( ! is_array( $user_id ) ) {
 			$cache = wp_cache_get( $user_id, 'bp_last_activity' );
 
 			if ( false !== $cache ) {
-				return $cache;
+				$retval[ $user_id ] = $cache;
+
+				return $retval;
 			}
 		}
 
@@ -1349,7 +1353,6 @@
 		$last_activities = $wpdb->get_results( $wpdb->prepare( "SELECT id, user_id, date_recorded FROM {$bp->members->table_name_last_activity} WHERE component = %s AND type = 'last_activity' AND user_id IN ({$user_ids_sql}) LIMIT {$user_count}", $bp->members->id ) );
 
 		// Re-key
-		$retval = array();
 		foreach ( $last_activities as $last_activity ) {
 			$retval[ $last_activity->user_id ] = array(
 				'user_id'       => $last_activity->user_id,