Shared libraries are no panacea for compatibility.
Turns out the new implementation of getpwnam left some file descriptors open. This resulted in a nice file descriptor leak in the parent, which sure enough threw up after it had been running for a while. As it happens, NIS can also be used to resolve machine names, and for a long time, Sun was pushing NIS big-time for just this use. Even so, NIS never really caught on for this use, perhaps because it doesn't scale well. There are, indeed, fairly persistant stories about people pumping all sorts of junk into named to confuse them, for various nefarious reasons.