multifile and discontiguous interaction

[bakaq]

If you mark a predicate as both multifile and discontiguous multiple times (as you would need to do in the case of generated code), the order in which you do so matters for some reason:

:- multifile(a/1).
:- discontiguous(a/1).
a(1).

:- multifile(a/1).
:- discontiguous(a/1).
a(2).

:- discontiguous(b/1).
:- multifile(b/1).
b(1).

:- discontiguous(b/1).
:- multifile(b/1).
b(2).

?- a(A).
   A = 2, unexpected.
?- b(B).
   B = 1
;  B = 2.