Nop, that undef's the hash, so the reference he keep in AoH points to a now undef'ed hash. He somehow need to disasociate the %globalHash name with the actual hash. Basically two ways of doing that if he wants to keep %globalHash truly global; using local or messing around with glob's

sunw287 ~ > perl -e '%globalHash=(one=>"two"); $ref=\%globalHash; unde
+f(%globalHash); print join("\n",keys %{$ref})'
sunw287 ~ >
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goldclaw