It doesn't make a lot of sense to use a loop variable that was previously declared, because the one that gets used within the loop is (temporarally), an entirely different variable, despite that it has the same name:

my $i = -23; 
for $i ( 1 .. 10 ) { 
    print $i; 
    last if $i == 5; 
} 
print $i;
1
2
3
4
5
-23
[download]

Doing so tends to make look as if $i will retain the last value used in the loop, but as you can see, it doesn't.

It caught me out a couple of times and is something that I hope will not persist into Perl6.

In fact, I think I would change it in perl 5.10. Any code that got bitten by the change in behaviour would be better changed anyway.