Open document opens new Window in IE which is in front, then back, front

Hello we have here the following Situation.

We have a big XI 3.1 Business Objects Platform running.

Also we have in our company net a portal in which the users can open reports from our BO platform.

This is done by usercustomized open document urls.

That al works fine.

Thing is, when a user requests the report, the Internet Explorer opens a new window which is blank. The Window can be seen for a second. Then the new window goes to the background behind the current window. After several seconds when in the new window the report starts to regenerate itself the window goes back to the front and the report is displayed.

And that behaviour confuses our user quite a lot.

The behaviour can be seen in IE 6 and 8. Firefox does not show this behavior.

IE9 wasn't tested.

So, does anyone know if there is an IE setting, or part of the Open document url which can change the behavior so that the new indow just apears and then stay apeared?

Changing the browser to firefox or IE9 is not an option because we are talking about 30k pc-clients.