NOTE- This article is no longer relevant once updating to Portal Framework version 5.0+.
There is a way to force the portal to load with the navigation collapsed. If you want the portal navigation hidden upon loading, you need to edit a single line of your DefaultPortalShell.aspx layout file.
1. Find the DefaultPortalShell.aspx & make a copy of the file. It is always recommended to backup portal files before editing them, in case something goes awry. Even though this may seem like a simple change, backing up the file is still a great idea.
Usually located here Drive:\Inetpub\wwwroot\Passageways\Layouts\Portal Shell Layouts\DefaultPortalShell.aspx
*Note that if you use a custom layout, you should edit that one instead of DefaultPortalShell.aspx
2. Open the file in notepad or a text editor
2a. Find the following tag:
<FRAMESET name="portalbottom" id="portalbottom" cols="0,250,*,0" border="1" frameborder="1" FRAMESPACING="6" TOPMARGIN="0" LEFTMARGIN="0" MARGINHEIGHT="0" MARGINWIDTH="0">
2b. Change the cols entry to "20,0,*,0" & save the file. Refresh the portal and it should start with the navigation collapsed!