Quick clicking gives strange page!

I've been seeing something just like this in a short HTML title that has a couple of test questions. When answering one of the questions I sometimes get a blank page with "true" in the top left corner (and BTW, these are mulitple choice questions, not true/false).Aaron's answer implies that this is caused by fast clicking. Is it always due to that, or are there other possible causes? I'm not clicking all that fast in my tests.

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