The hidden tab is where any bill that you've hidden will live, unless you decide to allow it back into your bill sheet. Watch this walkthrough for an explanation of the hidden tab.
When your bill sheet rolls over to a new session, any bills that you've hidden will stay on the hidden tab, which you may not want. There is an easy way, however, to manage your hidden bills and remove old bills from the hidden list that are no longer relevant. You can use the 'Clean All' or 'Clear All' buttons at the bottom of the screen:
The Clean All Button
This will remove any bills that no longer match your query - probably because your query doesn't match your current date range but maybe because you changed your state coverage.
The Clear All button
This will clear ALL the hidden bills. So click carefully!