Strange clipping at (0, 0)

Please have a look the following SVG file. It defines two symbols cross1
and cross2 which are then drawn on the canvas. What surprises me is that
the cross1 symbol does not render as cross, but only the parts with x>0
and y>0 are shown, like a clipping would occur even in the middle of the
page where the symbol is drawn. If I add 10 to each coordinate to
circumvent the negative coordinates (which is cross2), it is drawn
allright. This behaviour occurs when rendering with the Adobe and the
Batik viewer.
 
<?xml version="1.0" encoding="iso-8859-1"?>
<svg xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink" version="1.0">
 <defs>
     <symbol id="cross1">
     <line x1="0" y1="-10" x2="0" y2="10" stroke="red" stroke-width="1"
/>
    <line x1="-10" y1="0" x2="10" y2="0" stroke="blue" stroke-width="1"
/>
   </symbol>
     <symbol id="cross2">
     <line x1="10" y1="0" x2="10" y2="20" stroke="red" stroke-width="1"
/>
    <line x1="0" y1="10" x2="20" y2="10" stroke="blue" stroke-width="1"
/>
   </symbol>
 </defs>
 
  <use xlink:href="#cross1" transform="translate(50, 50)" />
  <use xlink:href="#cross2" transform="translate(100, 50)" />
</svg>

As I'm quite new to SVG, I suppose that I just miss a well-known points.
Thanks in advance.

Thomas


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