use current timestamp as initvars' variables,the krpano load xml become very slowly

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initvars:{timestamp:Date.parse(new Date())},

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<include url="test.xml?%$timestamp%" />

The above code is very very slowly.
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The following code is working fine.

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initvars:{timestamp:"1516535425"},

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<include url="test.xml?%$timestamp%" />

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why?