SOLVED

eog renders the marker incorrectly. Adding style="overflow:visible" to the marker's opening tag solves this.

Additionally, if you want the above example to render correctly in Batik, add gradientUnits to the gradient opening tag:
gradientUnits="userSpaceOnUse"

SOLVED: second post Software: Inkscape 0.47 on Ubuntu 9.10 64bit (the standard repository version). While hand-crafting a SVG image and trying to achieve "fading" lines with gradients, I've discovered that Inkscape and eog (the standard Gnome viewer) render my markers very differently. Fir...