When resolving both IPv4 and IPv6 and the answers from the DNS server are too big to fit together in the supplied buffer then a new buffer for the second answer is allocated by send_vc / send_dg, but _nss_dns_gethostbyname4_r fails to deallocate it. This is the only place where the resolver functions are called in such a way that they may work with two buffers.
http://permalink.gmane.org/gmane.comp.lib.glibc.alpha/39632 Fixed by d668061.
The patch was wrong.
Properly fixed by ab09bf6.
*** Bug 21336 has been marked as a duplicate of this bug. ***