Windows Phone set the font size for Thai in css


I have to show Thai and Roman text in a WebView (with NavigateToString). In CSS I've defined the font-sizes for Roman as 1.0em and for Thai as 1.8em. But Thai is displayed very small, smaller than Roman. If I set the font-size for Thai to 8em, then the result is about I want to have.

OK, I can set the font-size to 8.0. But if this wrong behavior an bug in the OS, and Microsoft correct it in the next version, then my customers will have Thai script in 800% that fills up the screen.

Is this a bug in the OS? Or am I missing something obvious?

Edit: this is the generated html

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<style type="text/css">

.Text     { font-size: 1.0em}
.News     { font-size: 1.0em; font-weight: bold; color: #333333}
.ThaiText { font-size: 2.0em; line-height: 2.2em;}
.TTiT     { font-size: 1.0em; line-height: 1.3em;}
.Tones    { font-size:80%; position:relative; bottom: 0.1em; letter-spacing: -0.15em; color: #FF0000;}
.Tonex    { font-size:80%; position:relative; bottom: 0.1em; letter-spacing: -0.15em; color: #00FF00;}
.NoWrap   { white-space:nowrap;}


<body bgcolor="#FFFFFF" text="#000000">

 <table width="100%" border="0" cellspacing="0" cellpadding="2">
   <td bgcolor="#00FF00">
    <p class="ThaiText">ไก่</p>
 <p class="News">Transcription</p>


It works on Internet Explorer and other browsers. Not in WebView on Windows Phone.

now I have found out that the problem is elsewhere.

My Thai text will be displayed in a table (just to colorize the background). And there lies the problem: the class definition in tables does not work as expected. This also applies to Roman text.

The text size is about 25% of the defined value. Outside tables everything is in order.