It must be an O::Deparse problem, as what's meant by %{{ }} = LIST isn't really all that odd. The construct: %{ ... } is simply a hash-dereference. Remember that the % just means a hash dereference on its own and that the braces serve as parenthetical operators with respect to references. Inside of the hash-dereference construct is just {} which is nothing more than an anonymous hash reference. So, %{{ }} is nothing more that an empty anonymous hash, in the same sense that @{[]} is an empty anonymous array.

Oh, and by the way, the issue at hand doesn't have anything to do with the fact that he uses an anonymous hash... you get the same behavior if you drop %x in in place of %{{ }}.