Sounds like a spectest is in order to prevent that case from happening, didn't see one in http://perlcabal.org/syn/S03.html (not that that's the definitive place to look for tests, but that's why I'm posting instead of DIY)
>However, I can well > imagine an implementation botching the cloning of the loop body by > assuming it's static and not cloning it. That would not be Perl 6, > since in Perl 6 every block is assumed to be a closure, and C<for> > is assumed to work just like C<map>, which will certainly clone > its closure....