This is really just a guess, but maybe the logic that disambiguates between defined-or and an empty m// regex (which I remember reading somewhere is fuzzy) is choosing to interpret it as a regex.

$ perl -MO=Deparse -e 'sub foo (&) {}; foo {"foo"} //'
Too many arguments for main::foo at -e line 1, at EOF
-e had compilation errors.
sub foo (&) {
}
&foo(sub {
    'foo';
}
, //);

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In reply to Re: BUG when parsing defined-or ? by Anonymous Monk
in thread BUG when parsing defined-or ? by LanX

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