Does IE 8 on Win 7 apply different security for internet vs intranet URLs in a trusted zone?

I have a situation where an ActiveX control is loaded into an iframe on a parent html page, and accessed by a child page.

In production, this ActiveX control isn't being loaded when accessed via IE 8 on Windows 7.

This same feature works properly when accessing the page on our intranet UAT environment on that same client machine and browser.

This feature also works properly when accessing the production location from a client running IE 8 on Windows XP.

In all situations, the URL is configured as a Trusted zone with the same security settings used, and protected mode is off on the Windows 7 machine.

To recap:

Win 7 + IE8 + Prod env = fail!

Win 7 + IE8 + UAT env = success!

XP + IE8 + Prod env = success!

It appears that the only difference in the equation is Windows 7 p开发者_运维技巧ointing at a public URL instead of an internal URL, since it works on Windows XP.

Are there known security differences in Windows 7 for this situation? Any other settings to look at? Thanks!

We stumbled upon a "solution" for this issue, but I don't understand the reasons why it worked, and aren't sure if it would solve other similar issues. In our case, adding some javascript to the child iframe to set the document.domain to a pingable URL resolved the issue. e.g. document.domain="yahoo.com";