Problem in comboBox

[Xcar]

hi,
I have the next problem ,
I have two combobox, the second combobox dependecy of first combobox ,
when a open la page for first time the second combobox show empty ,
when i select some item of first comboBox the second combobox load the data OK ..
but i have a button too but when a press the button i want load the data on the combobox but en the first comobox load fine the data and show text of combo ok but in the second comobox show the value , like that

1208

but if i press the button again the show correcty data in both comboxbox like that

1209

the code used when press the button is the next

fs.findField('empresa').setValue('SSG')
fs.findField('empresa').fireEvent('select');

fs.findField('marca').setValue('SSY');
fs.findField('marca').fireEvent('select');