Thanks for the logs and pcap you sent offlist. They were very helpful. I found the bug to be related to the headers your UA is sending. The UA is inserting Privacy and P-Preferred-Identity headers without a WSP after the COLON. This is in violation of the specs although I must admit it should be handled properly by the opensipstack parser. This is now fixed in CVS. Please download the latest opensipstack and retest. Post your results here. I am also pasting the RFC 3261 ABNF rule for HCOLON just in case you want to place a bug report to your UA manufacturer

Offending headers: "Privacy:none" "P-Preferred-Identity:6064443009 <sip:6064443009@xx.xx.xx.xx>"

RFC 3261

{noformat} SIP header field values can be folded onto multiple lines if the
continuation line begins with a space or horizontal tab. All linear
white space, including folding, has the same semantics as SP. A
recipient MAY replace any linear white space with a single SP before
interpreting the field value or forwarding the message downstream.
This is intended to behave exactly as HTTP/1.1 as described in RFC
2616 [8]. The SWS construct is used when linear white space is
optional, generally between tokens and separators.

LWS = [*WSP CRLF] 1*WSP ; linear whitespace
SWS = [LWS] ; sep whitespace

To separate the header name from the rest of value, a colon is used,
which, by the above rule, allows whitespace before, but no line
break, and whitespace after, including a linebreak. The HCOLON
defines this construct.

HCOLON = *( SP / HTAB ) ":" SWS
{noformat}