Dictionary / IdentityDictionary performance

I was surprised to that VWNC Dictionary /
IdentityDictionary performance seems to compare
unfavourably with GNU Smalltalk Dictionary performance
for this program - so I'm assuming that I've made a
dumb mistake writing the program, and I'd appreciate
it if someone could spot the mistake:

VWNC IdentityDictionary
http://shootout.alioth.debian.org/gp4/benchmark.php?test=knucleotide&lang=vw&id=0

VWNC Dictionary
http://shootout.alioth.debian.org/gp4/benchmark.php?test=knucleotide&lang=vw&id=2

GNU Smalltalk Dictionary
http://shootout.alioth.debian.org/gp4/benchmark.php?test=knucleotide&lang=gst&id=0

best wishes, Isaac

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