I have an application running on was 6, basically a form which user submits to the database, when the user tries to open two different browsers of the same form and upon acting on the form, the data entered in the form gets updated with the last modified on, means the data gets updated with the data entered in the other window.
There are many ways a session may get duplicated from one window to the next, or, potentially shared.
If each browser window is configured to create its own set of cookies, each window will have a unique session. Alternatively, if each window shares a cookie cache, both windows will share a common session. This of course, assumes you are using cookies for your session tracking. You could potentially be using URL re-writing as well.