I have find out that the LaTeX rendering effect doesn't work in the latest Inkscape. There is a patch which fixes the problem (see the URL). Because the pstoedit, which is available in the Portage Tree, doesn't support the option "-quite", I slightly modified the patch (see the inkscape-0.46-latex.patch in the attachment).
Created attachment 193583 [details, diff] inkscape-0.46-latex.patch Patch which fixes the LaTeX rendering problem.
Created attachment 193584 [details] inkscape-0.46-r5.ebuild.patch Patch for current inkscape-0.46-r5 ebuild.
this should be fixed in media-gfx/inkscape-0.47_pre1.