Javanese Tempius, Pedang Tusuk scabbard design question

[mross]

I just recently acquired this from Alam Shah. Thanks. I have a question on
the center part of the design. Any thoughts on why it is left plain? Alam, sent
me some urls' of others that share the same idea, so it seems to be a consistent pattern. So what are your thoughts?

PS The photos are from Alam. The can all be seen here;

http://www.kampungnet.com.sg/modules...view_album.php