On Ubuntu 12.04.3 x64 when you pull the network cable and let the connection sit idle, you'll get a SSL_ERROR_SYSCALL error in SSL_read when it detects the network break.  When the client learns of the network break and goes to tear down the connection, tls_disconnect gets called and it crashes in SSL_shutdown.  I don't know if this happens on every version of OpenSSL, but it definitely happens on Ubuntu 12.04.3 with all updates applied.