[Serusers] append_hf_helper brings strange characters.

I use the SER 0.10.99 version. I want to modify the procedure of tm module. Before sending the request and forwarding the reply, I managed to modify the request and response, f.e, to insert another header into the request and response. In the request, it works correctly.But in the response, sometime it works, sometimes it failed. The debug log is as follows. 2(2196) old size: 784, new size: 869 2(2196) build_res_from_sip_res: copied size: orig:76, new: 161, rest: 708 msg= SIP/2.0 200 OK^M 192.168.0.19:5500;branch=z9hG4bK1648283653^M Record-Route: <sip:192.168.0.19;ftag=549451184;lr>^M From: <sip:861111@sip.suntest.com>;tag=81929894;tag=549451184^M To: <sip:862222@sip.suntest.com>;tag=882426148^M Call-ID: 903055665(a)192.168.0.19^M CSeq: 21 INVITE^M Contact: <sip:862222@192.168.0.19:6600>^M Allow: INVITE, ACK, OPTIONS, CANCEL, BYE, SUBSCRIBE, NOTIFY, MESSAGE, INFO^M Content-Type: application/sdp^M Content-Length: 261^M ^M v=0^M o=nobody 20041028 20000001 IN IP4 192.168.0.19^M s=A call^M c=IN IP4 192.168.0.19^M t=1111396796 1111400396^M m=audio 7100 RTP/AVP 0 8^M a=rtpmap:0 PCMU/8000^M a=rtpmap:8 PCMA/8000^M m=video 7600 RTP/AVP 98 31^M a=rtpmap:98 H263/90000^M a=rtpmap:31 vf=4/CIF/1/768^M I insert the header "P-Security-Nobody: " into the response using the modified version of function "append_hf_helper". There are some strange code in the backend of inserted header. f.e, the italic black characters in the log. I had added a null terminator at the tail of the inserted header. I guess it is caused by the data_lump functions. Who can tell me the real reason of that? Thanks for your kind help. Best Regards. Sun Zongjun