diff -ruN linux-2.6.18/fs/unionfs/inode.c linux-2.6.18-modified/fs/unionfs/inode.c
--- linux-2.6.18/fs/unionfs/inode.c	2007-08-20 16:23:45 +0400
+++ linux-2.6.18-modified/fs/unionfs/inode.c	2007-08-20 16:20:44 +0400
@@ -85,7 +85,12 @@
 
 		newattrs.ia_mode = mode & ~current->fs->umask;
 		newattrs.ia_uid = current->fsuid;
-		newattrs.ia_gid = current->fsgid;
+		else if (parent->i_mode & S_ISGID) {
+			newattrs.i_gid = parent->i_gid;
+			if (S_ISDIR(mode))
+				mode |= S_ISGID;
+		} else
+			newattrs.ia_gid = current->fsgid;
 
 		if (wh_dentry->d_inode->i_size != 0) {
 			newattrs.ia_valid |= ATTR_SIZE;