diff -Naur thunar.old/thunar-file.c thunar/thunar-file.c
--- thunar.old/thunar-file.c	2006-04-23 21:17:31.000000000 +0200
+++ thunar/thunar-file.c	2006-04-23 21:08:48.000000000 +0200
@@ -507,7 +507,7 @@
       if (G_LIKELY (group != NULL))
         {
           /* check the group permissions */
-          groups = thunar_vfs_user_get_groups (user);
+          groups = thunar_vfs_user_get_groups (thunar_vfs_user_get_effective_user());
           for (lp = groups; lp != NULL; lp = lp->next)
             if (THUNAR_VFS_GROUP (lp->data) == group)
               {