HOTFIX: The text size that you specify is not applied to all IE7 windows that you open on a Windows Vista-based computer
This problem occurs if the following conditions are true:
• Protected mode is enabled in Internet Explorer 7.
• The window in which you specify the text size contains Web pages that use an encoding type other than UTF-8 encoding, such as Shift-JIS character encoding.
Note this problem does not affect Windows XP or Windows Server 2003
http://support.microsoft.com/default.aspx/kb/939944