According to the source code, its not a fixed size, its set to 100%, this could be your issue, i did find its no repeating, it only does it on occasion.
Code:
<td width="469" height="137" align="left" valign="top"><img src="tren_z/misc/tren_z_header_top_ls.jpg" width="469" height="137" alt="" /></td>
<td width="100%" height="137" align="left" valign="top" style="background-image: url(tren_z/misc/tren_z_header_top_back.jpg)"><img src="tren_z/misc/tren_z_header_top_back.jpg" width="100%" height="137" alt="" /></td>
<td width="40" height="137" align="left" valign="top"><img src="tren_z/misc/tren_z_header_rs.jpg" width="40" height="137" alt="" /></td>