The Poco::Net::SocketAddress::operator < () is flawed, doesn't produce a strict weak ordering and therefore the SocketAddress cannot be used as a key in std::map. There are pairs of addresses for which the expression ((Addr1 < Addr2) && (Addr2 < Addr1)) is true, for example:
Addr1("10.0.0.1:2000");
Addr2("10.0.0.2:1000");

The operator needs to check the components for equality, too, before going to a deeper component.

Found in version 1.4.6.