Difference when opening page in a new tab and new window

I have a web page that starts a lengthy process (creating some files that can last for 1/2 hour).


I noticed the following behavior of IE 7 and I'm not sure if it's normal or not.
I open the page and start the process (click on the button on the page). If I try to open this page or any other page that belongs to the same project in a new tab, the page doesn't open until the process started is not finished.


But, if I try to open the same page in a new window, regardless of the fact that the process is still running in another window, it opens immediately.


Any explanations?

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