This may be waaay off and a longshot, but you know what this looks like to me... just mathematically speaking...  
Like a graphical representation of a rounding error - being that it's so rhytmic in appearance, and considering that poser works with rather small units to start with, one idea that pops into my head is that maybe it runs out of significant figures to calculate a smooth transition.
I don't hve clue how to test that theory though... but maybe it gives you some inew ideas...

this sort of gave me the idea:  http://www.softimage.com/community/xsi/discuss/archives/xsi.archive.0607/msg00749.htm
Maybe it gives you more clues then it did to me....

Hi, my namez: "NO, Bad Kitteh, NO!"  Whaz yurs?
BadKittehCo Store  BadKittehCo Freebies and product support