From @masak

<masak> rakudo​: class A { method foo(A :$a) { say $a.WHAT } }; A.new.foo
<p6eval> rakudo 72f914​: OUTPUT«Any()␤»
<masak> jnthn​: has this been reported? the fact that $a is of a type
that wouldn't bind?
<jnthn> masak​: Looks odd.
* masak submits rakudobug
<jnthn> Is it peculiar to nameds?
<ash__> rakudo​: class A {}; sub foo(A :$a) { say $a.WHAT }; foo;
<p6eval> rakudo 72f914​: OUTPUT«Any()␤»
<masak> so, not specific to nameds.
<jnthn> oh good
<jnthn> It's an easy fix then, I expect.
* jnthn is a little surprised we musta gone many months with this bug.
<masak> jnthn​: we have too few spectests :)
<masak> rakudo​: sub foo(Int $a = "OH HAI") { say $a }; foo
<p6eval> rakudo 72f914​: OUTPUT«OH HAI␤»
<masak> that was fun, too :)

From @moritz

This first issue is now gone, $a is initialized to the A type object.
The second issue still remains.

The RT System itself - Status changed from 'new' to 'open'

From @moritz

Fixed now, and tested in S06-signature/optional.t

@moritz - Status changed from 'open' to 'resolved'