I think that it means that foreach (#blah alah blah) created an anonymous array, that can be reused :) I don't know if it is a bug or a feature of Perl :)

The anonymous array is not created only in the case of for(number..number), as ikegami mentioned, as such loops are replaced by counting ones.

The shortest illustrating example:

for (0..2) {
  foreach my $x (0..1, ()) { print +($x .= " wassap? ") . "\n"; }
}
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It prints:

0 wassap?
1 wassap?
0 wassap?  wassap?
1 wassap?  wassap?
0 wassap?  wassap?  wassap?
1 wassap?  wassap?  wassap?
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UPDATE:

B::Deparse displays that it ocuurs only to arrays generated by the .. operator.

UPDATE 2:

I just realised that i used the feature of modifyable '..' arrays in my code :)

print map { s/$/\n/;$_ } (0..1);
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works, while

print map { s/$/\n/;$_ } (0,1);
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produces a fatal error :) So we can create one more example:

for (0..1) {
    print map { s/$/!\n/;$_ } (0..1);
}
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The bug is that anonymous arrays created by .. are globally scoped :) and I don't think it'a an optimisation for Perl.

Finally, i think that the title of the node is incorrect :)). The good title would be Unexpected behavior of '..' lists. Or smth like this :)