The other syntax - the one perl is guessing wrong - is @{foo} being a form of the array @foo. Perl is not looking first for a builtin function there, but a bareword.

You can use parens as you did, or place a harmless operator in front of the shift.

my @shift = qw/a shifty array/;
sub foo {
    print @{shift};
    my @vars = @{+shift};
    print @{vars}
}
foo [qw/A mere example/];
__END__
[download]

which prints, ashiftyarrayAmereexample