This goes back to the Cold War, back when Germany was surrounded by communist controlled countries, the West Germans had a policy of moving some of it's gold stores abroad and further West, fearing there might one day be an attack by Russian and the other Eastern Bloc countries.
Now they don't fear it as much now, so they want their cash back
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Edit - This is common in Europe and many other countries that where bordered by unstable governments. Canada, US, England, and France were traditionally seen as safer countries, so portions of many nation's golds reserves are split amongst banks in those areas.