BDC Unable to populate the field for transaction code LT04

All,

I have created a BDC for the transaction code LT04, in that for the field 'Foreground/Background' i have passed 'H' (Foreground) in the recording. Through i am populating 'H'(Foreground) it does take the 'System_Guided' as input while processing. BDC is not taking the populated value. Any suggestion to populate the value.

Thanks in advance.

    bdc_dynpro( exporting iv_program = 'SAPML03T'
                          iv_dynpro  = '0131'
                changing  ct_bdcdata = lt_bdcdata ).
    bdc_field( exporting iv_fnam    = 'LTAK-LGNUM'
                         iv_fval    = '240'
               changing  ct_bdcdata = lt_bdcdata ).
    clear lv_fval.
    lv_fval = lv_tbnum.
    bdc_field( exporting iv_fnam    = 'LTBK-TBNUM'
                         iv_fval    = lv_fval
               changing  ct_bdcdata = lt_bdcdata ).
    bdc_field( exporting iv_fnam    = '*LTBP-TBPOS'
                         iv_fval    = space
               changing  ct_bdcdata = lt_bdcdata ).

    constants: foreground type lvs_dunkl value 'H'. 
    clear lv_fval.
    lv_fval = foreground.
    bdc_field( exporting iv_fnam    = 'RL03T-DUNKL'
                         iv_fval    = lv_fval           "<--Passing 'H'
               changing  ct_bdcdata = lt_bdcdata ).