Flex使用宋体渲染越南语显示错误

本来应该显示Lưu nhóm，偏偏编译后显示Lưu nhòm。二声变成了四声，并且某些情况下，刚打开的窗口时二声的，然后变成了四声。初始以为是Flex的问题，分别使用S和mx包下的Label做实验，后发现是默认字体宋体导致的。

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
               xmlns:s="library://ns.adobe.com/flex/spark"
               xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600">
    <fx:Metadata>
        [ResourceBundle("conference")]
    </fx:Metadata>

    <fx:Script>
        <![CDATA[

            protected function button1_clickHandler(event:MouseEvent):void
            {
                resourceManager.localeChain = ["en_US"];
            }
            protected function button1_clickHandler2(event:MouseEvent):void
            {
                resourceManager.localeChain = ["zh_CN"];
            }

            [Bindable]
            private var sfW:String;
            [Bindable]
            private var sfS:Number;
            [Bindable]
            private var sfF:String;

        ]]>
    </fx:Script>

    <fx:Declarations>
        <!-- 将非可视元素（例如服务、值对象）放在此处 -->
    </fx:Declarations>
    <s:VGroup>
        <s:Spacer height="20"/>
        <s:VGroup>
            <s:Label fontWeight="bold" fontSize="14" fontFamily="Tahoma"
                     text="{resourceManager.getString('conference','title.savegroup')}"/>
            <mx:Label fontWeight="bold" fontSize="14" fontFamily="Tahoma"
                      text="{resourceManager.getString('conference','title.savegroup')}"/>

            <s:Label fontWeight="bold" fontSize="14" fontFamily="宋体"
                     text="{resourceManager.getString('conference','title.savegroup')}"/>
            <mx:Label fontWeight="bold" fontSize="14" fontFamily="宋体"
                      text="{resourceManager.getString('conference','title.savegroup')}"/>

            <s:Label fontWeight="{sfW}" fontSize="{sfS}" fontFamily="{sfF}"
                     text="{resourceManager.getString('conference','title.savegroup')}"/>
            <mx:Label fontWeight="{sfW}" fontSize="{sfS}" fontFamily="{sfF}"
                      text="{resourceManager.getString('conference','title.savegroup')}"/>
        </s:VGroup>
        <s:Button label="en" click="button1_clickHandler(event)"/>
        <s:Button label="cn" click="button1_clickHandler2(event)"/>
        <s:HGroup>
            <s:CheckBox label="fontWeight-bold" change="sfW=sfW=='bold'?null:'bold'"/>
            <s:CheckBox label="fontSize-14" change="sfS=sfS==14?12:14"/>
            <s:CheckBox label="fontFamily-宋体" change="sfF=sfF=='宋体'?null:'宋体'"/>
        </s:HGroup>
    </s:VGroup>
</s:Application>

语言包：

title.savegroup=Lưu nhóm

默认字体改为越南文的Tahoma，即解决问题。以下截图，每两行一组。第一组是Tahoma字体，第二组是宋体，第三组是动态切换的。结论与加粗和字号无关，与字体有关。