Initially under FreeBSD-9.2, ports devel/py-qt4 and misc/py-qt4-doc failed to install with an error similar to that referenced here. Passing the NO_STAGE variable works similarly for both of these.
I'm not clear on whether the error is related to the fact that I'm using pkgng.
make -DNO_STAGE install clean worked. I'm not clear on whether the error is related to the fact that I'm using pkgng.