Output histogram gets 'choppy', don't understand why

[Nocturnal]

Hi,

I was doing some histogram work on one of my images and noticed that the output histogram has some odd 'dips' in it, illustrated here:

http://gallery.tungstentech.com/main.php?g2_itemId=1059

I hope this is normal and explainable but I don't understand how this can happen. Is my input range too restricted to allow a smooth output histogram? I took a small section of the image and saved it here:

http://cid-a93625fef5ca95fb.skydrive.live.com/self.aspx/PixInsight/choppy-source.zip

I hope you can provide some insight.