aha-- woke up and realized what I was doing-- definitely an ID 10-T error. Most of my keys were one letter, but one was actually a full word (I know the possible keys ahead of time), so I did something stupid like 
hash =
{
    a=>[];
    b=>[]
    c=>[]
   .
   .
   .
}

#some time later
my $key = "alpha"
my $array = $hash->{$key};

[download]

At this point there isn't anything at $hash->{$key}, so $array isn't pointing to anything real. When I push onto $array, that memory will get allocated happily, and won't create anything in the hash (which is a very good thing). If instead, the first thing I do is to shove something into @{$hash->{$key}}, a new entry gets magically allocated, and then everything works as expected.

Obviously I'm not one with the perl yet.

In reply to Re^3: creating defined references to arrays of size zero by spieper
in thread creating defined references to arrays of size zero by spieper

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