We have troubles with the ListView of a Combobox, when trying to avoid showing the Scrollbar.
Following sample illustrates the problem:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class ComboBoxSample extends Application {

    @Override public void start(Stage stage) {

        final ComboBox testComboBoxOK = new ComboBox();
        String values[] = {"1","2","3","4","5","6","7","8","9","10","11","12"};

        testComboBoxOK.getItems().addAll(values);
        testComboBoxOK.setVisibleRowCount(values.length);

        final ComboBox testComboBoxWrong = new ComboBox();
        testComboBoxWrong.getItems().addAll(values);
        testComboBoxWrong.getItems().add("13");
        testComboBoxWrong.setVisibleRowCount(values.length + 1);

        HBox horizontalBox = new HBox();
        horizontalBox.setSpacing(10.0);
        horizontalBox.getChildren().addAll(testComboBoxOK, testComboBoxWrong);

        Scene scene = new Scene(horizontalBox, 450, 250);
        stage.setScene(scene);
        stage.show();
    }
}

When using a stylesheet like the one below it gets worse:

.combo-box-popup .list-cell{
    -fx-text-fill: blue;
    -fx-background-color: yellow;
    -fx-border-color: red;
    -fx-border-width: 10 10 0 10;
}