Unwanted divider between header and table in Android

Question

I am developing an Android app and I created a TableLayout to display some information, but the table I created has a grey divider between the table header and the rest of the rows that gets bigger the more records there are on the table.

This is how the table looks with 20~ rows

I just created a TableLayout inside of some other containers like so:

FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".fragmentos.TablaAsig">

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <HorizontalScrollView
                android:layout_width="match_parent"
                android:layout_height="match_parent">

                <LinearLayout
                    android:layout_width="wrap_content"
                    android:layout_height="match_parent"
                    android:orientation="vertical">

                    <TableLayout
                        android:id="@+id/tablaSinAsig"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:layout_marginLeft="50dp"
                        android:layout_marginTop="10dp"
                        android:layout_marginBottom="40dp"
                        android:divider="?android:listDivider"
                        android:paddingBottom="60dp"
                        android:showDividers="middle">

                        <!-- Header de la tabla -->

                        <TableRow
                            android:layout_marginLeft="10dp"
                            android:layout_marginRight="10dp"
                            android:background="@android:color/holo_red_dark"
                            android:padding="10dp">


                            <TextView
                                android:layout_width="wrap_content"
                                android:layout_height="wrap_content"
                                android:layout_marginRight="15dp"
                                android:text="Asignatu gabeko TAG-ak" />
                        </TableRow>
                    </TableLayout>
                </LinearLayout>
            </HorizontalScrollView>

        </LinearLayout>
    </ScrollView>
</FrameLayout>

And I have a function that creates new TableRows to insert into this TableLayout:

public void poblarTablaSinAsig(Context context, TableLayout tableLayout){
        tagsSinAsig = new ArrayList<String>();
        SQLiteDatabase db = this.getWritableDatabase();

        int filas = tableLayout.getChildCount();
        for (int i = 1; i < filas; i++) {
            View child = tableLayout.getChildAt(i);
            if (child instanceof TableRow) ((ViewGroup) child).removeAllViews();
        }

        for(int i = 0; i < EventHandler.allTagData.size(); i++) {
            TableRow nuevoReg = new TableRow(context);
            TextView codTag = new TextView(context);

            TableRow.LayoutParams parametros = new TableRow.LayoutParams(
                    TableRow.LayoutParams.MATCH_PARENT,
                    TableRow.LayoutParams.WRAP_CONTENT
            );

            parametros.setMargins(50, 15, 10, 15);
            nuevoReg.setLayoutParams(parametros);


            Cursor cursor = null;
            String query = "SELECT * FROM asignaciones WHERE CodigoChip = '" +  EventHandler.allTagData.get(i) + "'";
            cursor = db.rawQuery(query, null);

            if(cursor.getCount() <= 0) {
                codTag.setText(EventHandler.allTagData.get(i));
                nuevoReg.addView(codTag, parametros);
                tableLayout.addView(nuevoReg, parametros);
                tagsSinAsig.add(EventHandler.allTagData.get(i));
            } else {
                tagsAsig.add(EventHandler.allTagData.get(i));
                }
            }
    }

Where is this weird divider being created? How can I solve the problem?