Index: wp-includes/plugin.php
===================================================================
--- wp-includes/plugin.php	(revision 19471)
+++ wp-includes/plugin.php	(working copy)
@@ -566,7 +566,7 @@
 	$plugin_dir = preg_replace('|/+|','/', $plugin_dir); // remove any duplicate slash
 	$mu_plugin_dir = str_replace('\\','/',WPMU_PLUGIN_DIR); // sanitize for Win32 installs
 	$mu_plugin_dir = preg_replace('|/+|','/', $mu_plugin_dir); // remove any duplicate slash
-	$file = preg_replace('#^' . preg_quote($plugin_dir, '#') . '/|^' . preg_quote($mu_plugin_dir, '#') . '/#','',$file); // get relative path from plugins dir
+	$file = preg_replace('#^' . preg_quote($plugin_dir, '#') . '|^' . preg_quote($mu_plugin_dir, '#') . '#','',$file); // get relative path from plugins dir
 	$file = trim($file, '/');
 	return $file;
 }