[perl #125658] [BUG] Cannot use multi methods in Roles

[via RT]

# New Ticket Created by  Adriaan Larmuseau 
# Please include the string:  [perl #125658]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=125658 >


Bug report #124393 states that one cannot use stub multi methods in roles,
but multi methods do not work with roles in general.
Consider the following example:

role A {
  multi method a(Int , Int --> Mu:D) { False };
  multi method a(Bool:D $handle, Int $int --> Mu:D) { False };
}

class Test does A {
  multi method a(Int $stream, Int $int) { True }
  multi method a(Bool:D $handle, Int $int) { True }
}

# test
my $test = Test.new();
my Bool $b = True;
$test.a($b,5);

Produces the following output:

Ambiguous call to 'a'; these signatures all match:
:(Test $: Bool:D $handle, Int $int, *%_)
:(Test $: Bool:D $handle, Int $int, *%_)
  in block <unit> at test.pl:17

For perl6 --version:
This is perl6 version 2015.06-293-g27f88c4 built on MoarVM version
2015.06-98-gf22142b