You made me curious, especially since here at work I'm investigating the possibility of using YAML to serialize some data. So I installed YAML::Syck and tried it on the same data as the OP:

$ perl -MYAML::Syck -le 'print Dump { zip => "07102" }'
---
zip: 07102
[download]

So the behaviour is just the same. But I also get

$ perl -MData::Dumper -MYAML::Syck -le 'print Dumper Load Dump { zip =
+> "07102" }'
$VAR1 = {
          'zip' => '07102'
        };
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which is not what he fears. That only happens if $YAML::Syck::ImplicitTyping is set to a true value (by default, it's false):

$ perl -MData::Dumper -MYAML::Syck -le '$YAML::Syck::ImplicitTyping=1;
print Dumper Load Dump { zip => "07102" }'
$VAR1 = {
          'zip' => 3650
        };
[download]