Inconsistent result with GnuProlo / Ubuntu 10.04/64 bits

Hi,
I've got inconsistent results with gnu Prolog, with a simple nqueens
program:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%
queens(N,L):-
	length(L,N),fd_domain(L,1,N) ,
	fd_all_different(L),correct(L),
	fd_labelingff(L).

correct([]).
correct([X|L]):-
	safe_diag_fd(X,L,1),correct(L).

safe_diag_fd(X,[],_).
safe_diag_fd(X,[Y|L],D):-
	 Y-X #\= D,
	 X-Y #\= D,
	 D1 is D+1,
	 safe_diag_fd(X,L,D1).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%

For queens(32,L) , I have duplicate values in the list, and sometimes -1 in
the following answers:
| ?- queens(32,L).
L =
[1,3,5,16,15,4,10,7,13,16,22,15,6,17,19,21,8,25,2,16,27,28,9,18,20,14,11,13,10,2,2,12]
? 
yes
| ?- queens(32,L),sort0(L).
L =
[1,2,2,2,3,4,5,6,7,8,9,10,10,11,12,13,13,14,15,15,16,16,16,17,18,19,20,21,22,25,27,28]
? ;
L =
[-1,1,2,2,3,4,5,6,7,8,9,10,10,11,12,13,13,14,15,15,16,16,16,17,18,19,20,21,22,25,27,28]
? ;
L =
[-1,1,2,2,3,4,5,6,7,8,9,10,10,11,12,13,13,14,15,15,16,16,16,17,18,19,20,21,22,25,27,28]
? 

I'm running gnuProlog 1.3.0 under Ubuntu 10.04 / 64 bits. Don't seem to have
the same problem on another computer under Debian Lenny.

Any suggestion?
Regards,
Steve.


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