Some users can run afoul of Portal's user-agent rules. Symptoms include the inability to log in and form submissions just causing page refreshes where all the form data is lost.
The problem is an intersection of two things:
- Pestware installed in the browser that changes the user-agent.
- WebSphere Portal misinterpreting the user-agent type and altering application behaviour.
See Technote 1441915 for IBM's support analysis.