IE and OWA

We are implementing a new portal at work and we have linked the email "link"
in the portal (Luminis from Sungard SCT) to launch OWA. If you select log off
from within OWA and click on the "X" to close the window, the minute you go
back to the portal and try to move around in the portal, you get
disconnected. This only happens with Internet Explorer. If you open IE first
and log into OWA and then go to File, New, Window, go to the portal URL and
login. If you go back to the original OWA window and log off and click the
"X" for the OWA window, you get disconnected when you go back to the IE
protal window. So it appears to be something in how IE windows are tied
together. The log off from OWA is killing the Luminis portal section and I am
trying to find a way to identify the cause and how to "turn it off". If you
open a fresh session of IE and OWA and then open a seperate fresh session of
IE and Luminis, this scenario does not happen and you can move about in the
portal.
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Dwight