Several of our Solaris sparc RPM 2.5.6 machines dumped core as we tried to upgrade a package. It was one particular package which caused the core dump and this only on some machines. The coredump occured very early in the installation (but I could hear the disk on the ftp site moving). The problem went away when we did an 'rpm --rebuilddb', so I have a workaround.
This problem appears to be solved.