Mine seems to do this on cold starts. Not sure about seeing the RPMs go up that much, but I can hear it going: "rrrrrr----rrrmmm---rrrrrrrrr----rrrmmmmm" (this is at idle). Once at operating temperature it stops though.
I think the range of +- 500hp might be a little high, if not unintentionally exaggerated, but cold starts definitely have a bit of RPM hop to them sometimes. Albeit minimal, it's not abnormal unless it's noticeably drastic.