Thats because your trying to goto a block that looks like it would be optimized out of existance.

That sounds like a nice explanation; however, the following script panics with the same message if there is a "1" in the command line:

use feature qw(say switch);

for my $data (@ARGV) {
    given($data) {
        when (1) { say 'one'; goto two;  }
        when (2) { two: say 'two' ;      }
        default  { say 'something else'; }
    }
}
[download]