Pop up way too fast

NetSuite,

How can I let pop up NOT to interrupt my process of selecting items in the dropdown?

Maybe someone can help me out:

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The following works fine. When I type "U", the dropdown will bring me to the first country started with "U" and I can browse down to select others started with "U"
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if(name == 'custentity_stu_nationality')
    {  
        var nationality = nlapiGetFieldText('custentity_stu_nationality');
        var dualNations = nlapiGetFieldText('custentity130');     
        if(nationality == "United States")
        {
           


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But the following does now work fine with a pop up, when I type "U", the pop up already shows up and the dropdown shrinks back to the original.