That behavior is, at least, fully documented. for loop variables are always localized (or lexically declared) to the block. Predicate-for cannot have a named loop variable. (Note: my situation did not concern itself with loop variables, but lexicals declared in the list of a block-for are scoped to the block, while those in a predicate-for are scoped to the enclosing block/file)

It might be nice to expand the syntax to allow a reference to a scalar variable to be given as the loop variable, and the referenced variable would be used instead of a newly-created variable.

my $i = 123;
for \$i ( 0 .. 10 ) {
    last if $i == 5;
}

print $i;
__END__
5
[download]

The present situation provides a use for a C-style for loop:

my $i = 123;
for ($i = 0; $i <= 10; ++$i) {
    last if $i == 5;
}

print $i;
__END__
5
[download]