{ curley braces } build a hash reference. Your code to "zero" out %data is being treated equivalent to %data = ( {}, undef ). In other words: $data{ {} } = undef. The {} is getting stringifed to HASH(0x...) and its value in %data is undefined. Hashes always start empty, so declaring them with my %hash; or just start using it, and it will be empty as you expect. If you need to clear out a hash, do %hash = (); (parens, denoting an empty list).

Whenever you see anything strange with you code, your first debugging step should ALWAYS be to run with warnings enabled ('use warnings' or -w flag to Perl), assuming you aren't running with them turned on to begin with. Bonus if your code compiles cleanly with strict turned on too (as it should!). With warnings enabled, you would have seen this: 

Reference found where even-sized list expected at script line n.

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In reply to Re: Odd hash problem. by Fastolfe
in thread Odd hash problem. by onion2k

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