mptcp SYN message transfer issue

[Jian Zhu]

Hi, all:
   I download mptcp implementation provided by Dr.Kheirkhah (https://github.com/mkheirkhah/mptcp).
   When i run the example(src/scratch/mptcp.cc) on two different ubuntu machines(name the machine as M1, M2), something strange happened:
   In M1, the log shows that two nodes(name one node as A, and another node as B) perform as the mptcp protocol (i.e. initiate connection, start subflow and transfer data).
   However, the log generated in M2 shows that:
   A sends SYN (with MP_CAPABLE OPTION) to B, when B receives SYN, the log show that the SYN is without MP_CAPABLE option.
   I am so confused why the MP_CAPABLE Option is lost and where it is lost?

   I have checked the code running on two machines and there is no any difference.
  
   The configuration of the two machines is with some difference:
   On Machine M1, I run ./waf configure with following output:
   Checking for 'gtk+-2.0' >= 2.12                                                                  : yes
   Checking for 'libxml-2.0' >= 2.7                                                                 : yes
   On Machine M2, I run ./waf configure with following output:
   Checking for 'gtk+-2.0' >= 2.12                                                                  : not found
   Checking for 'libxml-2.0' >= 2.7                                                                 :  not found
   I am not sure whether this is the reason for the MP_CAPABLE option missing i described above.

   I am a newb to NS3, can anyone kind tell me how to identify the reason for what happened in M2?