Tasking troubles, unexpected termination.

[Shark8 <onewingedshark@gmail.com>]

with
Ada.Text_IO,
Ada.Calendar,
Ada.Containers.Indefinite_Vectors;

Procedure Scheduling is

    -- Introduce shorthand so convert Strings to access strings.
    Function "+" (Item : String) Return Not Null Access String is
      ( New String'(Item) );
    
    -- Forward declare the Notification type; indicate it has discriminants.
    Type Notification(<>);
    
    -- Declare Handle for Notifications.
    Type Notification_Handle is Not Null Access Notification;
    
    Type Notification(	Message	: Not Null Access String;
			Expiry	: Not Null Access Ada.Calendar.Time
		     ) is null record;
    
    -- Declare the Timing-task.
    Task Type Timing ( Resolution : Not Null Access Duration ) is
	Entry Add( Event : Notification_Handle );
    end Timing;


    -- Implementation for the timing-task.
    Task body Timing is
	-- Internal package, defining Vectors holding notification handles.
	Package Notification_Vector is New Ada.Containers.Indefinite_Vectors
	  ( Index_Type => Positive, Element_Type => Notification_Handle );
	Use Notification_Vector;
	
	-- Declare a Vector to hold all the notifications.
	Notification_List : Vector:= Empty_Vector;
	
	Procedure Handle_Expiration is
	    Use Ada.Calendar, Ada.Text_IO;
	    Length : Positive:= Positive(Notification_List.Length);
	    Now    : Time:= Clock;
	begin
	    -- Iterate through the vector's elements; reversed so that deletion
	    -- does not intefere with the iteration.
	    for Index in reverse 1..Length loop
		declare
		    Item : Notification_Handle Renames Notification_List(Index);
		begin
		    -- If it's reached the expiry, then we display the message
		    -- and remove the item.
		    if Now > Item.Expiry.All then
			Put_Line( "Message: " & Item.Message.All);
			Notification_List.Delete(Index);
		    end if;
		end;
	    end loop;
	    
	    declare
		Post_op_length : Positive:= Positive(Notification_List.Length);
	    begin
		if Length /= post_op_length then
		    Put_Line( "Deleted items; New Length:" &  post_op_length'Img);
		end if;
	    end;
	end Handle_Expiration;

	Use Ada.Containers;
    begin
	-- When there are no items in our internal vector, then we need can only
	-- accept Add or terminate the task.
	-- When we add an item, then we can either add another item or when the
	-- time expires iterate the vector and handling Notifications as needed.
	loop
	    select 
		accept Add( Event : Notification_Handle ) do
		    Notification_List.Append( Event );
		end add;
		while not Notification_List.Is_Empty loop
		    Handle_Expiration;
		    select
			accept Add( Event : Notification_Handle ) do
			    Notification_List.Append( Event );
			    Ada.Text_IO.Put_Line( "New Length: " & Notification_List.Length'Img );
			end add;
		    or
			delay Timing.Resolution.All;
		    end select;
		end loop;
		Ada.Text_IO.Put_Line( "EMPTY. Length: " & Notification_List.Length'Img );
	    or
		terminate;
	    end select;
	end loop;
    end Timing;
    
    
    K : Timing( Resolution => New Duration'(2.0) );
    
begin
    For Index in 1..10 loop
	declare
	    Use Ada.Calendar;
	    Expire : Time:= Clock + (Index*2.0); -- Now and 2*Index seconds.
	    Item : Notification(
			 Message => + ("DD"&Positive'Image(Index)),
			 Expiry  => New Time'( Expire )
			);
	begin
	    K.Add( Event => New Notification'(Item) );
	end;
    end loop;
end Scheduling;

----------------------------------

Output:
C:\Programming\Projects\Scheduler>scheduling.exe
New Length:  2
New Length:  3
New Length:  4
New Length:  5
New Length:  6
New Length:  7
New Length:  8
New Length:  9
New Length:  10
Message: DD 10


As you can see there's something happening to force termination -- there should at the least be an new-length message -- this leads me to believe [or, more accurately, guess] that there's some exception happening in the task which is blowing everything up.

Is that the case?
Also, if there is some tasking-exceptions interaction, how do I force them to display [and/or handle them] instead of falling off a cliff?