alt-shift-< and alt-shift-> are supposed to shift through a series of fonts in rxvt. This is a build option that we have always enabled in the past, and we should contine to do so. Many of us rxvt users depend on it.
I'll do this one, I've done it before...
Fixed in rxvt-2.6.PRE2-3 (also added missing rxvt man page while I was at it :-)