document.open ignores window features in .HTA on Windows 7 when url is local intranet

Question

This code open(sUrl,'','width=791,height=550,left=800,top=0',true); works as expected from a .HTA on XP/IE8.

It also works as expected from a .HTM on XP/IE8 as well as Windows 7/IE8

However IF sUrl points to a site listed in IE's Local Intranet Security Zone when used in a .HTA on Windows 7/IE8 it then opens sUrl but it does so in a default-sized and placed browser window. That is, it ignores 'width=791,height=550,left=800,top=0'

All works fine everywhere when sUrl points to an Internet site.

I can't find an answer but I did find someone else asking the question so at least I'm not alone.

Thanks for any tips you may have.