Sorry. My example was wrong. Here another one. C<a([])> executes as intended but C<@t> does not. I find that unintuitive.
cat mmd5.pm6
multi sub a(@a) { say 1 ~ @a.perl }
multi sub a([]) { say 2 ~ [].perl }
my @t=(1,2);
a([]);
a(@t)
$ perl6 mmd5.pm6
2[]
No applicable candidates found to dispatch to for 'a'. Available candidates are:
:(@a)
:(Positional ())
in main program body at line 5:mmd5.pm6
$
