busybox nslookup slow on x86_64

[muddyboot]

Hi, I found nslookup resolve very slow on x86_64 system , it cost 5 seconds or longer almost everytime.

Tested OS: Debian 7 x86_64 with kernel 3.2.5 &  LFS x86_64 with kernel 3.12

No IPv6 enabled in kernel config.
DNS server works fine
nslookup program from bind-9.7 works fine
nslookup from busybox test on i686 system OK

target busybox version: 1.17.4、1.20.2、1.21.1、1.22.1

Any response for this problem is great appreciated.