Some IO rule prevent write on their input data member.

Using the source file and selection xml attached along side the HepMC 2 library, the example fails (m_barcode is incorrectly stored) because:

   i= 9, m_barcode       type=  3, offset=144, len=1, method=0 [cached]

   i=10, m_barcode       type=  3, offset=  0, len=1, method=0 [write]

   i=11, m_barcode       type=1000, offset=136, len=1, method=0

where the element '10' used for write has (incorrectly) an offset set to 0.