As it turns out, the libraries were installed in a number of places (e.g. libpng not only in /usr/local/lib but also in /usr/lib in the chroot). In one of those places, there was still an old copy of librrd.so.3.0, which referenced the libraries that I was seeing errors for. I cleaned everything up and now it works.
Seems that my mistake was using the install_rrdtool.sh script to copy the libraries when I set it up initially (and it put everything in /usr/lib instead of mirroring the hierarchy that ldd reports) and then doing the update manually (and mirroring the hierarchy, thus creating duplicates). Sorry for the noise, Lars
