[perl #130396] [BUG] =:= operation aginst item contextualized object returns incorrect result

[Moritz Lenz via RT]

This is not a bug. $b is a container that contains the array @a, so @a !=:= $b.
:
An easy test is assigning to $b, and see if it's reflected in @a:

$ perl6 -e 'my @a = 1,2; my $b = @a.item; $b = 42; say @a'
[1 2]