As a status update: I don't get a segfault in the REPL with a current rakudo
(tested on moar, parrot and jvm).
The error message has changed slightly:
$ perl6-m
> class Foo { has Hash of Hash $.foo = {} }; Foo.new
Type check failed in assignment to '$!foo'; expected 'Hash[Hash]' but got 'Hash'
in block at src/gen/m-CORE.setting:1018
in method BUILDALL at src/gen/m-CORE.setting:973
in method bless at src/gen/m-CORE.setting:961
in method new at src/gen/m-CORE.setting:947
in block <unit> at <unknown file>:1
> say "alive"
alive
> exit
$
