[OpenSBC] How to eliminate MERGED REQUEST error

[msp <pm...@gm...>]

Hi all,
I have done below setup by minor modification in OSBC code.

------>| OpenSBC | ----------> | OpenSIP |
<------|                 | <---------- |                |

When calls come from outside net to OSBC, OSBC adds the IP address of source
in custom SIP header variable "SRC-URI" (for that I done minor midificaiton
in *SBCRoutingHandler.cxx*) and route the call to OpenSIP.

OpenSIP find out route based on custom SIP header variable "SRC-URI", and
add the destination URI as custom SIP header variable "SBC-Force-Route",
route the call back to OpenSBC.
So that OpenSBC should route the call to uri set in "SBC-Force-Route"
variable.

But when I tested with sample calls, OSBC route the call to OpenSIP that
part work well, but when call comes from OpenSIP (by SBC-Force-Route set to
proper URI), OSBC does not route the call, and end up with below messages:

========================================================================
*2009/03/13 15:05:40.394 DTL: [CID=0x0ba2] Event: ---> Inbound - INVITE
sip:1010@192.168.1.81:5060 SIP/2.0
2009/03/13 15:05:40.394 DBG: [CID=0x0ba2] *** MESSAGE ARRIVAL *** for SIP
Session 7c15bd8907fcb0251b2bbbd47301ca1d@192.168.1.23-0x001e
2009/03/13 15:05:40.394 ERR: [CID=0x0ba2] *** MERGED REQUEST DETECTED
***INVITE sip:1010@192.168.1.81:5060 SIP/2.0
2009/03/13 15:05:40.395 INF: [CID=0x0ba2] *** NO ROUTE ** URI
sip:1010@192.168.1.81:5060through local registration database
===================================================================================

I have attached whole log in pastebin, you can find it on link:
*http://pastebin.com/f1f3a843b

What should I do to eliminate error "Merged Request..."?

Thanks,
Shehzad