Sharepoint issue for F5 configuration

If you haven't already, please carefully review information from Microsoft about Alternate Access Mapping (AAM) configuration on Sharepoint. It's critical that this be configured correctly so that the host header and port of the application presented from the F5 is understood by Sharepoint server. The problem you describe sounds like this is not configured correctly.

Here's a good document on it:

http://gallery.technet.microsoft.com/The-final-guide-to-551bd75b