for Sales order the tax number1(STCD1) not populating in IDOC

Hi All,

I am having an issue in IDOC. For one Order no(VA02), in sold-to-party, if the fields Telex number and Teletex number are empty then for the generated idoc no, the field Tax number1(STCD1) is being populated. And for another Order No. this is vice versa. How to find how the field STCD1 is populating? Please help me in solving this.

Thanks,
Haritha