<svg width="800" height="128" xmlns="http://www.w3.org/2000/svg">
  <defs>
  <filter id="testFilter" filterUnits="objectBoundingBox" x="0%" y="0%" width="100%" height="100%" >
    <feConvolveMatrix order="3 8" kernelMatrix="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0" targetY="7" preserveAlpha="true" />
  </filter>
  </defs>

 <!-- Both shapes should look identical -->
 <!-- Expected -->
 <rect x="0" y="0" width="800" height="48" fill="#0000FF" />
 <g>
  <rect x="0" y="16" width="800" height="16" fill="#00FF00" />
 </g>

 <!-- Actual -->
 <rect x="0" y="80" width="800" height="48" fill="#0000FF" />
 <g filter="url(#testFilter)">
  <rect x="0" y="96" width="800" height="16" fill="#00FF00" />
 </g>

</svg>