/usr/bin/urxvt -pixmap '/path/to/background/image.xpm' (version x11-terms/rxvt-unicode-8.4) now returns urxvt: "pixmap": unknown or malformed option. urxvt: "/path/to/background/image.xpm": malformed option. Reproducible: Always Comparing the distributions for 8.4 and 8.3, this seems to be because -pixmap now requires libAfterImage while in 8.3 libXpm may have been enough: configure.ac: AC_DEFINE(XPM_BACKGROUND, 1, Define if you want to have sexy-looking background pixmaps. Needs libXpm or libAfterImage) has become in 8.4: configure.ac: AC_DEFINE(BG_IMAGE_FROM_FILE, 1, Define if you want to have sexy-looking background pixmaps. Needs libAfterImage) Meanwhile media-libs/libafterimage is not depended by the ebuild and is masked anyway (don't know why, maybe just not used much). That's as far as I got. Don't take it for granted that the difference above is the problem and the entire problem. I'll probably revert to 8.3 for now.
*** This bug has been marked as a duplicate of bug 198944 ***