you need to be more clear on when you say deselect an item! when selecting is it a radio button for filtering? or checkboxes?
you should read up on this: the main part is:
To enable the clearing of a filter so that users can see all the
values in the List View Web Part, select Allow Multiple selections. In
this case, the Select Filter Value(s) dialog box displays check boxes,
rather than radio buttons.
Note You cannot use this feature to display the filtered results of
two or more selections, because The List View Web Part does not
support multiple selections. If a user chooses multiple selections,
only the first selection is used.
you need to find the advanced filter options:
If you selected the Allow Multiple selections property, to redisplay
all the values in the List View Web Part, the user must clear all the
check boxes in the Select Filter Value(s) dialog box, and then click
in your case deselecting will/should show no results as there is nothing selected!
look under Connect a SharePoint List Filter Web Part to a List View Web Part
you should be able to connect your list (a) by using SharePoint List Filter Web Part to connect to list (b) that is filtered with custom items ;)