The "show only new articles" button becomes permanent for a group
if the button is active and a different group is selected.  After returning to
the first group, the effect of the "only new articles" button cannot be
undone except by selecting "Match Read" and "Match Unread" in the Filter
menu.  The following patch seems to fix this for me...

--- filter-mediator.c,0	2003-08-14 10:48:41.000000000 -0400
+++ filter-mediator.c	2004-05-26 21:52:59.000000000 -0400
@@ -257,6 +257,9 @@ show_only_new_tb_cb (GtkToggleButton * t
 
 	if (active)
 		_menu_new_bits = _filter_bits & NEW_MASK;
+	else
+		if (_menu_new_bits == STATE_FILTER_NEW)
+			_menu_new_bits = NEW_MASK;
 
 	set_mask_bits (NEW_MASK, active ? STATE_FILTER_NEW : _menu_new_bits);
 }