I'm trying to use the Humanity icon set in KDE 4.3. Humanity is the new default icons for Ubuntu 9.10, so they're designed with Gnome in mind. They look fine in Gnome, but when I use them in KDE there are some obvious rendering errors. I'm not sure if this is a bug in KDE, or a bug in the SVG icons that somehow doesn't show up in Gnome. Here's a screenshot of Dolphin showing quite a few of these problems. Note the arrows for the back and forward buttons, the Home folder icon, Trash, Volume (ntfs), My Book, and the play button for the preview.

The Qt SVG renderer is known to cause problems sometimes, it implements the SVG 1.2 Tiny standard.
I'm not really up to date regarding Qt's SVG component. What I do know is that development is still going on, and there are improvements in the engine for the soon-to-be-released Qt 4.6. So you could give that a try when it's released.
Otherwise I'm afraid you're out of luck.

Good to know this is worked on, as I am having the exact same issue.

Converted the Humanity Theme to work with KDE4:

http://kde-look.org/content/show.php?content=114842