[Linux] Split menu button border becomes weird when control looses focus

To reproduce click the "Button" button.

package splitmenubuttonsample;

import com.sun.javafx.runtime.VersionInfo;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.MenuItem;
import javafx.scene.control.SplitMenuButton;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class SplitMenuButtonSample extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        HBox hb = new HBox(5);
        
        SplitMenuButton smb = new SplitMenuButton();
        smb.setText("Menu button");
        
        smb.getItems().addAll(new MenuItem("test1"), new MenuItem("test2"));
        
        hb.getChildren().add(smb);
        
        Button btn = new Button("Button");
        
        hb.getChildren().add(btn);
        
        Scene scene = new Scene(hb);
        stage.setTitle(VersionInfo.getRuntimeVersion());
        stage.setScene(scene);
        stage.show();
    }
}