Only some fuzzy msgid have the old string?

I was pleased to see the old msgid in comment for fuzzy strings. This
really helps to see what has changed in the original text. But why is
this really helpful thing missing from some msgids that are marked
fuzzy?

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Tapio Lehtonen
tapio.lehtonen <at> iki.fi
http://www.iki.fi/tapio.lehtonen