IE7 ProcID changes on Page-Redirect

First of all: sorry about my poor english.

I have a problem with IE7 under Vista. For a own software project i
generate a html-page with an redirect via javascript (that's 'cause
there are post data inside the page). My programm starts a browser an
waits for some reason for the process handle of the created browser to
be closed.

Under XP for all IE browser versions, including IE7 this works fine.
Under Vista it seems to be, that the started browser executes the
javascript closes itself and starts a new browser for the redirected
page. This means the process handle of the first browser was closed.
In the taskmanager you can track this by looking at the process id!

Now the curiosity: Logging in as Administrator - not a member of group
administrators, but the real Administrator - this does not happen, the
started browser is always the same after the page redirect!!!

This, i guess, means that there is any option, any setting, any system
policy, so i can switch this behavior for normal users too.

Can anyone give me a useful hint how to do this. Of course complte
disabling UAC works also, but that is no option for me, because the
lack of security.

Greetings from Germany
MIKE