Thanks for the iOS 6.0.1 update. The 'view all' filter works well!
For other filters like '(overdue, today) & p1' the web version of this works perfectly, but the iOS app adds some extra tasks in there that are not p1 tasks. It looks like p1 and today is correct, but all overdue are included and not just p1 tasks that are overdue.
Also the filter '(overdue, today) & (p1, p2)' to show all p1 or p2 tasks that are due today or overdue produces similar results to the point above. p1 and p2 today are shown, but all overdue tasks are shown. Also this filter has crashed the app a few times, but not every time.