Thanks Daniel. I followed your advice and install kamailio 3.1. Now I get a weird problem: it works 1 out 5 times for the relaying.

The t_relay is where the the problem is, because I check the response code and route(LOCATION) always succeeds, which means the entries exist in "location". If I don't put set_forward_no_connect, then t_relay will take a long time until my client time out. If I put it, then the client will get 477 right away. BTW, the original config didn't work, either. That's why I started to strip down some irrelevant stuff.