Top level: underscore variables incorrect

[UWN]

?- term_variables(_+_,L).
   L = [_], unexpected.
   L = [_A,_B]. % expected but not found

[UWN]

Shorter:

?- _==_.
   true, unexpected.
   false. % expected

[UWN]

Yet,

?- _=1,_=2.
   true. % as expected

[pmoura]

Shorter:

?- _==_.
   true, unexpected.
   false. % expected

Could this be a top-level issue? Logtalk includes this test and it passes with the latest Tau Prolog git version. Moreover:

?- A == B.
false

?- _ == _.
true

?- assertz((t :- _ == _)).
true

?- t.
false

[UWN]

?- copy_term(_+_,T).
   T = __1+__2. % expected, perfect!

[UWN]

   ?- sort([_,_],L).
   L = [_], unexpected.

[UWN]

?- X=_,Y=_,L=X-X.
   X = Y, _ = Y, L = Y-Y, unexpected.

(All examples, I enter at the first page directly. So the prompt there is actually ">" and the answers are given in reverse order on the right...)