On Windows with trunk, I try to login to linkedin but after entering valid credentials it present me a page asking me to "Join LinkedIn Today". Both in Chrome and QtWebKit bring me to http://www.linkedin.com/home after login, except that with QtWebKit, I'm not logged in.
Confirmed on Linux.
This issue is not reproducible in rekonq but was in Arora and in the Demo Browser, which mostly share the same cookie jar code. Probably not a QtWebKit bug, closing it.