Description of problem:
If you try to access several portal pages at once in different tabs of your browser (i.e. multiple requests from the same session), you will end up with unexpected content in your tabs as the requests get mixed.

Steps to Reproduce:
1. Open several tabs with different portal pages in your browser.
2. Refresh all the tabs at once (or just open them quickly after each other).
  
Actual results:
The content in the tabs is not what you expected, i.e. you see different pages (from different tabs) under incorrect tabs/URLs or a page with portlets showing content from their instances in other tabs (like navigation pointing to a different location etc.). Try repeating the action causing this and you will get different pages as the requests interleave in a different way.

Expected results:
Each window/tab shows the right content and is not influenced by other requests.

Additional info:
Reproduced in latest Chrome and FF to rule out a browser problem.