Form dropdown field value resets after scrolling PDF

The dropdown field that resets is a dependent dropdown, ruled by antoher dropdown.

The custom javascript (I got from the internet) from this dropdown is:

var dependentListBoxFieldName = "dependentDropdown2";

var dependentListValues =

{

    "FALK 1000-TR": [

        ["1000-TR 40-75 - RC=2,16", "1000-TR 40-75 - RC=2,16"],   

          ["1000-TR 50-85 - RC=2,61", "1000-TR 50-85 - RC=2,61"],

          ["1000-TR 60-95 - RC=3,05", "1000-TR 60-95 - RC=3,05"],

          ["1000-TR 80-115 - RC=3,99", "1000-TR 80-115 - RC=3,99"],

          ["1000-TR 100-135 - RC=4,92", "1000-TR 100-135 - RC=4,92"],

          ["1000-TR 125-160 - RC=6,06", "1000-TR 125-160 - RC=6,06"],

          ["1000-TR 150-185 - RC=7,17", "1000-TR 150-185 - RC=7,17"]

    ],

    "FALK 1100-TR3+": [

         ["1100-TR 3+ 40-70 - RC=2,07", "1100-TR 3+ 40-70 - RC=2,07"],   

          ["1100-TR 3+ 50-80 - RC=2,52", "1100-TR 3+ 50-80 - RC=2,52"],

          ["1100-TR 3+ 60-90 - RC=2,99", "1100-TR 3+ 60-90 - RC=2,99"],

          ["1100-TR 3+ 80-110 - RC=3,91", "1100-TR 3+ 80-110 - RC=3,91"],

          ["1100-TR 3+ 100-130 - RC=4,82", "1100-TR 3+ 100-130 - RC=4,82"],

          ["1100-TR 3+ 130-160 - RC=6,17", "1100-TR 3+ 130-160 - RC=6,17"],

          ["1100-TR 3+ 150-180 - RC=7,07", "1100-TR 3+ 150-180 - RC=7,07"]

    ],

    "FALK 1000-GL": [

        ["1000-GL 43-83 - RC=2,52", "1000-GL 43-83 - RC=2,52"],

        ["1000-GL 60-100 - RC=3,31", "1000-GL 60-100 - RC=3,31"],

        ["1000-GL 80-120 - RC=4,26", "1000-GL 80-120 - RC=4,26"],

        ["1000-GL 120-160 - RC=6,14", "1000-GL 120-160 - RC=6,14"]

    ],

    "Specials": [

    ["FALK 1140-KV 80 - RC=3,67", "FALK 1140-KV 80 - RC=3,67"],   

    ["FALK 1140-KV 100 - RC=4,61", "FALK 1140-KV 100 - RC=4,61"],   

    ["FALK 1140-KV 120 - RC=5,55", "FALK 1140-KV 120 - RC=5,55"],   

    ["FALK 1140-KV 140 - RC=6,50", "FALK 1140-KV 140 - RC=6,50"],   

    ["FALK 1060-WB 60 - RC=2,61", "FALK 1060-WB 60 - RC=2,61"],   

       ["FALK 1060-WB 80 - RC=3,55", "FALK 1060-WB 80 - RC=3,55"],   

       ["FALK 1060-WB 100 - RC=4,50", "FALK 1060-WB 100 - RC=4,50"],   

       ["FALK 1060-WB 120 - RC=5,45", "FALK 1060-WB 120 - RC=5,45"],   

       ["FALK 1060-WB 140 - RC=6,40", "FALK 1060-WB 140 - RC=6,40"],   

       ["FALK 1060-WB 160 - RC=7,35", "FALK 1060-WB 160 - RC=7,35"]

    ]

};

if ((event.target.type == "combobox" && event.name == "Format") || (event.target.type == "listbox" && event.name == "Keystroke")) {

    if (event.target.type == "combobox") {

        if (dependentListValues.hasOwnProperty(event.target.value)) {

            this.getField(dependentListBoxFieldName).setItems(dependentListValues[event.target.value]);

        }

        else {

            this.getField(dependentListBoxFieldName).clearItems();

        }

    }

    if (event.target.type == "listbox" && dependentListValues.hasOwnProperty(event.changeEx)) {

        this.getField(dependentListBoxFieldName).setItems(dependentListValues[event.changeEx]);   

    }

}

else {

    app.alert("This script was not intended for this field type or event.");   

}

Maybe it has something to do with this code??