Upgrade switched to Install


I have successfully upgraded 2 out of my 3 forums to RC3. However on the 3rd one, when I go to /install/ I get prompted that my environment meets all the requirements and it will begin the installation. I tried to move a bit forward than that and it is indeed a new installation which will require me to drop all tables.

Any pointers on how i can make the system think that this is really an upgrade and not a new installation?