Android工具栏：横向模式下的小标题文本

我正在测试Android上的新工具栏和AppCompat主题，但遇到了问题。我的工具栏标题文本在纵向模式下看起来是正常大小，但在横向模式下却变得很小，尽管我在代码中未做任何更改标题文本大小的操作。以下是屏幕截图：

activity_main.xml：

<!-- A DrawerLayout is intended to be used as the top-level content view using match_parent for both width and height to consume the full space available. -->
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="com.techfunmyanmar.jujaka.ui.MainActivity">

    <android.support.v7.widget.Toolbar
        android:id="@+id/main_toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

    <android.support.v4.widget.DrawerLayout
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!-- As the main content view, the view below consumes the entire
             space available using match_parent in both dimensions. -->
        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

        <!-- android:layout_gravity="start" tells DrawerLayout to treat
             this as a sliding drawer on the left side for left-to-right
             languages and on the right side for right-to-left languages.
             If you're not building against API 17 or higher, use
             android:layout_gravity="left" instead. -->
        <!-- The drawer is given a fixed width in dp and extends the full height of
             the container. -->
        <fragment
            android:id="@+id/navigation_drawer"
            android:name="com.techfunmyanmar.jujaka.ui.NavigationDrawerFragment"
            android:layout_width="@dimen/navigation_drawer_width"
            android:layout_height="match_parent"
            android:layout_gravity="start"
            tools:layout="@layout/fragment_navigation_drawer" />
    </android.support.v4.widget.DrawerLayout>
</LinearLayout>

styles.xml：

<resources>
    <!-- Base application theme. -->
    <style name="AppBaseTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <item name="windowActionBar">false</item>

        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/primary</item>
        <item name="colorPrimaryDark">@color/primary_dark</item>
        <item name="colorAccent">@color/accent</item>

    </style>

    <!-- Main application theme. -->
    <style name="AppTheme" parent="AppBaseTheme">

    </style>

    <style name="DrawerArrowStyle" parent="Widget.AppCompat.DrawerArrowToggle">
        <item name="spinBars">true</item>
    </style>
</resources>