Beat slicer on Djm 2000 off sync with traktor (video link inc)

Here is a video of my issue with the beat slice function once it's run with a tune from traktor.

i have tried - auto/tap beat, master sync, Chanel sync, and manual but it seams to record just one beat more than needed.

all tunes have been analysed through tractor and are perfect as far as I can tell.

in the video it seams only slightly off sync but 9 times out of ten it sounds a complete car crash. It doesn't happen when using record box however I'm sure it is designed to work with any input. 

https://youtu.be/OpxfX-827Ww