Good process of testing and deduction. Deductive reasoning like that is one of those qualities present in programmers who are capable of solving problems on their own. I believe logical and deductive reasoning is an attribute that must accompany success as a programmer. Your testing can be summarized well by perlref:

WARNING

You may not (usefully) use a reference as the key to a hash. It will be converted into a string:

    $x{ \$a } = $a;
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If you try to dereference the key, it won't do a hard dereference, and you won't accomplish what you're attempting. You might want to do something more like

    $r = \@a;
    $x{ $r } = $r;
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And then at least you can use the values(), which will be real refs, instead of the keys(), which won't.

The standard Tie::RefHash module provides a convenient workaround to this.

References are passed around as scalars, but keys are indices composed of string values, not full scalar citizens.