When I run your code, I get the extremely helpful error message:

Can't locate object method "Value" via package "Tie::IxHash"
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Change:

print $r->Value('a') ; # doesn't work
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to:

print $r->Values('a') ;
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According to the Tie::IxHash module docs, the name of the function is 'Values' (with an 's'), and it prints '1' for me.