GRE Over MPLS On 7600 Not Working

A question posted on netpro about GRE-MPLS tunnel which was not working end to end but PE-CE communication was there. The connectivity was depicted

CE1--PE1--P--PE2(7600)--CE2

GRE MPLS tunnel from CE2 to 7600 and 7600 onwards it becomes a part of MPLS. So traffic will like this; PE1 to PE2 it's a MPLS traffic and from PE2 to Ce2 it is a IP traffic. The analysis shown by one of my friend is that CE2 was replying to the packets sent by PE1. The weird is that MPLS to IP conversion is happening properlly but for reverse traffic IP to MPLS is not happening.
The first solution I posted that SIP 400 was required to bind tunnels but the analysis shown by friend steered me. During googling I found the solution on Cisco Site that there is command which need to be enabled on 7600 because it corrupts the ip packets.
Command is "mls mpls tunnel-recir"

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