Why WMP calls the IFileSourceFilter's Load fn Twice

Why WMP calls the IFileSourceFilter's Load fn Twice:
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if we implemented the IFileSourceFilter in our Filter, WMP calls the IFileSourceFilter's Load() function twice;

Reason:
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 WMP calls "Load" two times, First time just to check whether the filter is proper dll or not
 WMP call "Load" again for the second time. Second time only  we have to create any pins to the Filter;
In case of Source Filter,we will be creating pins only at the second time;