[perl #131207] [REGEX] unexpected NFA

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$ uname -a
Linux stretch 4.9.0-2-686-pae #1 SMP Debian 4.9.18-1 (2017-03-30) i686 GNU/Linux
$ perl6 --version
This is Rakudo version 2017.04.2-22-g9ed89d947 built on MoarVM version 2017.04
implementing Perl 6.c.
$ cat test.p6
say grammar {
    rule TOP { <foo> | <bar> }
    rule foo { foo ** 2..* % \, }
    rule bar { bar }
}.parse: "foo,foo"
$ perl6 test.p6
Invalid to edge 0 in NFA statelist
  in regex TOP at test.p6 line 2
  in block <unit> at test.p6 line 1